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The Journal of Clinical Endocrinology & Metabolism Vol. 86, No. 8 3525-3532
Copyright © 2001 by The Endocrine Society


Endocrine Care

Thyroid Function and Autoimmunity during Interferon ß-1b Treatment: A Multicenter Prospective Study

Luca Durelli, Bruno Ferrero, Alessandra Oggero, Elisabetta Verdun, Angelo Ghezzi, Enrico Montanari, Mauro Zaffaroni and the Betaferon Safety Trial Study Group

Clinica Neurologica, Dipartimento di Neuroscienze, Universitá di Torino (L.D., B.F., A.O., E.V.); Divisione di Neurologia, Ospedale di Gallarate (A.G., M.Z.); Divisione di Neurologia, Ospedale di Fidenza (E.M.), I-10126 Torino, Italy

Address all correspondence and requests for reprints to: Luca Durelli, M.D., Clinica Neurologica, Dipartimento di Neuroscienze, Universita’ di Torino, Via Cherasco 15, I-10126 Torino, Italy.

Abstract

Thyroid dysfunction and autoimmunity have been reported during type I interferon therapy, namely interferon-{alpha} for chronic hepatitis or interferon-ß for multiple sclerosis. To define the frequency of thyroid dysfunction and autoimmunity during interferon-ß treatment, 156 multiple sclerosis patients were prospectively followed up by 18 centers for 1 yr after starting interferon-ß-1b treatment. Serial clinical assessments and tests of thyroid and liver function and antithyroid autoantibodies (all performed by the same centralized laboratory) were conducted every 3 months. TSH and antithyroid autoantibodies against human TG or thyroid microsomal antigens were measured by immunoradiometric methods; free T3 and T4 were measured by chromatographic assays. Longitudinal occurrence of thyroid or liver alterations or of autoantibodies was analyzed with the generalized estimating equations method, correcting for the correlation of repeated measurements of the same subject over time. Pretreatment comparison with a control group of 437 healthy blood donors did not show significant differences in the frequency of thyroid dysfunction or antithyroid autoantibody positivity. During interferon-ß treatment, the de novo frequency of thyroid alteration was 8.3%, that of liver alteration was 37.5%, and that of antithyroid autoantibody was 4.5%. Generalized estimating equations analysis demonstrated that the frequency of liver alteration significantly increased during treatment compared with the baseline value (odds ratio, 7.03; confidence interval, 2.49–19.9), whereas that of thyroid alteration or of antithyroid autoantibodies did not. The frequency of thyroid dysfunction during interferon-ß treatment showed random, nonsignificant changes over time and, in addition, was not correlated to antithyroid autoantibody positivity.

THYROID DYSFUNCTION and autoimmunity have been reported during chronic type I interferon (IFN) therapy, more often in patients positive for antithyroid (AT) autoantibodies (autoAb) (1, 2, 3, 4, 5). Most reports describe patients treated with IFN{alpha} for chronic hepatitis C, a disease that seems to predispose to autoimmunity (6, 7). In such patients thyroid dysfunction or autoimmunity would contraindicate IFN treatment (1, 8). IFNß is the first approved treatment for multiple sclerosis (MS), an immune-mediated disease (9), and AT autoAb and thyroid dysfunctions have been recently reported in MS patients treated with IFNß (10, 11, 12, 13, 14). Most of those reports advise frequent thyroid function and autoAb testing during IFNß treatment. In addition, IFNß is being tested in a randomized clinical trial of chronic hepatitis patients (15, 16).

To define the frequency of thyroid dysfunction and autoimmunity during IFNß treatment, we conducted a multicenter prospective follow-up of MS patients recruited by 18 Italian centers. To take into account the correlation of repeated measurements of the same subject over time, longitudinal data were analyzed with the generalized estimating equations (GEE) method (17).

Subjects and Methods

Subjects and treatment

One hundred and fifty-six patients (101 women and 55 men) with clinically definite relapsing-remitting MS (18), 2 clinically documented exacerbations during the preceding 2 yr, and no exacerbation (and no corticosteroid treatment) for at least 30 d before entry into the study were prospectively included between February 1996 and March 1997 by 18 MS centers representative of northern, central, and southern Italy. Exclusion criteria included pregnancy, lactation, unwillingness to practice acceptable birth control, major depression or suicidal attempt in medical history, and clinically significant heart, liver, renal, or bone marrow disease. The presence of thyroid disease was not an exclusion criteria. IFNß-1b (Betaferon, Schering AG, Berlin, Germany) was given sc on alternate days at a dose of 8 million IU. Patients were examined twice a month during first month, once a month during second and third months, and thereafter every 3 months or in the event of MS exacerbations or side-effects. Follow-up ranged from 12–15 months. Baseline thyroid function and autoimmunity were compared with those of 437 healthy blood donors (162 women). Their serum samples were prospectively collected by blood banks of the hospitals of the 18 MS centers during the same period of MS patient recruitment. Subjects with clinically overt thyroid dysfunction, goiter, or personal or family history of thyroid disease were excluded from the control sample, which was, therefore, a population of clinically normothyroidal individuals. Informed consent was obtained in all cases.

Laboratory methods

Hematological investigations, repeated at baseline and each planned visit for 1 yr, were all performed in the same laboratory (Laboratorio Baldi e Riberi, Ospedale Maggiore S. Giovanni Battista, Torino, Italy).

Thyroid function evaluation. TSH was measured by a sensitive immunoradiometric method (Biocode, Sclessin, Belgium), using mouse antihuman TSH monoclonal antibody (Ab) as substrate, and mouse [125I]antihuman TSH Ab as tracer. Purified human TSH standard solutions were calibrated against the Medical Research Council 80/558 international standard. Samples from patients or standards and a fixed amount of tracer were added to assay tubes coated with mouse antihuman TSH monoclonal Ab. Unbound Ab was then discarded, and the remaining radioactivity was counted. The TSH concentration in the sample was interpolated from the calibration curve and expressed in milliinternational units (mIU) per liter. The intra- and interassay coefficients of variation for the TSH assay were 3.9–6.2% and 4.2–7.1%, respectively. The limit of detectability was 0.02 mIU/liter. The normal range (as derived from the 95% confidence limits of measurements obtained for healthy normothyroidal individuals) was 0.3–3 mIU/liter.

Free T3 (fT3) and T4 (fT4) were measured by chromatographic assays (Technogenetics, Cassina de Pecchi, Italy). Patient serum samples or negative or positive standards were added to chromatographic columns with Sephadex LH-20. Chromatographic separation on Sephadex produces highly purified hormones, giving the assay more specificity compared with methods where unpurified serum is directly added to the RIA (19, 20). Adsorbed hormones were, then, directly collected into LISO-PHASE chromatographic columns containing anti-fT3 or anti-fT4 rabbit Ab bound to Sepharose CL-4B gel as immunoadsorbent. A fixed amount of [125I]fT3 or [125I]fT4, which was used as radioactive tracer, and a fixed amount of anti-fT3 or anti-fT4 Ab, used as immunoreagents, were added. Antigen-Ab complex was bound to the immunoadsorbent by affinity chromatography; unbound hormones were discarded, and the remaining radioactivity was counted. The sample fT3 or fT4 concentration was interpolated from the calibration curves. Intra- and interassay coefficients of variation for the fT3 method were 3.5–5.8% and 6.5–9.8%, respectively (limit of detectability, 0.3 ng/liter). Intra- and interassay coefficients of variation for the fT4 method were 3.7–6.5% and 5–7.5%, respectively (limit of detectability, 3 ng/dl). The normal range (95% confidence limits of measurements obtained for healthy normothyroidal individuals) for fT3 was 2.2–4.4 ng/liter; that for fT4 was 7–19 ng/dl.

AT autoAb against human TG (TGA) or thyroid microsomal antigens (TMA) were detected by the immunoradiometric method (Biocode, Sclessin, Belgium), using purified human TGA or TMA as substrates, and Staphylococcus aureus [125I]protein A as tracer. A fixed amount of a 1:50 dilution in PBS of patient serum samples or of human TGA or TMA serum standard solutions (calibrated against Medical Research Council human TGA 65/93 or human TMA 66/387 international standards) was added to assay tubes coated with highly purified human TGA or TMA. The sample anti-TGA or anti-TMA autoAb concentration was interpolated from the calibration curves and expressed as international units per ml. Intra- and interassay coefficients of variation for the anti-TGA autoAb method were 3.7–7.2% and 7.2–9.2%, respectively (limit of detectability, 3 IU/ml). Intra- and interassay coefficients of variation for the anti-TMA autoAb method were 4.2–8.1% and 7.9–13.8%, respectively (limit of detectability, 2.5 IU/ml). AT autoAb were considered positive when their level was above 100 IU/ml.

Thyroid function alteration was classified according to the American Thyroid Association guidelines (21, 22): clinically overt hyperthyroidism, undetectable to less than 0.1 mIU/liter TSH, more than 4.4 ng/liter fT3, or more than 19 ng/dl fT4; subclinical hyperthyroidism, undetectable to less than 0.1 mIU/liter TSH and fT3 and fT4 in the normal range without exogenous T4 intake; clinically overt hypothyroidism, TSH above the upper limit of the normal range (3 mIU/liter in our assay) and fT4 below 7 ng/dl; and subclinical hypothyroidism, TSH above the upper limit of the normal range and fT4 in the normal range.

Liver function evaluation included serum bilirubin, hepatic cytolytic (aspartate and alanine aminotransferases) and cholestatic ({gamma}-glutamyl transpeptidase and alkaline phosphatase) enzymes, and hepatic synthetic function indicators, such as albumin, fibrinogen, prothrombin time, and partial thromboplastin time. Markers of viral hepatitis B or C were tested with immunological sensitive PCR-based assays in patients with liver function alteration.

Statistical analysis

Baseline comparison with healthy normothyroidal controls. To carefully compare in MS patients and controls even subtle abnormalities of thyroid function, cases were stratified for several progressively decreasing or increasing cut-off values of TSH (0.1, 0.3, 3, and 5 mIU/liter; Table 1Go). Due to the different gender and age distribution of the two groups, odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using logistic regression with the different TSH cut-off values as dependent variables and MS, gender, and age as independent variables. In a separate regression model, anti-TMA autoAb positivity was also added as independent variable.


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Table 1. Frequency of thyroid-related hormone abnormalities and of antithyroid microsomal antigen autoantibody positivity in MS patients and healthy controls

 
Longitudinal evaluation during IFNß treatment. Observations taken at baseline and at months 3, 6, 9, and 12 were included in the analysis. De novo occurrence of an alteration was evaluated only in patients normal for that parameter at the baseline observation. The total number of observations at each time point may, therefore, change accordingly, and it is always indicated in the text or tables. Frequencies of alterations were compared using Fisher’s exact test or {chi}2 test with Yates’ correction for continuity. In addition, the frequency of de novo occurring alterations during treatment was compared with baseline frequency for the whole 12-month study period as well as for each 3-month interval using McNemar’s test. To describe the association between the occurrence of thyroid function alteration and the occurrence of AT autoAb, {phi} correlation coefficients were calculated. Furthermore, between subgroups of patients with AT autoAb negativity or positivity at baseline or at any time during study, the proportion of patients with newly occurring thyroid alterations during treatment was compared using Fisher’s test or {chi}2 test with Yates’ correction for continuity. A longitudinal analysis with the GEE approach (17) was used to address the question of whether the probability of having liver, thyroid, or autoAb alterations varies with time during treatment compared with baseline by taking into account the correlation of repeated observations. Longitudinal data require special statistical methods because the set of observations of one subject tends to be intercorrelated. The GEE approach provides asymptotically valid inference even when the correlation structure of repeated observations is unknown. We analyzed as a response variable the presence/absence of liver, thyroid, or autoAb alteration, and the OR was the odds of alterations among patients at each time point divided by the odds among patients at baseline. A patient was considered to have liver alteration when he had at least one liver function parameter altered (increase in liver enzymes or alteration of hepatic synthetic function indicators 15% out of normal range); a patient was considered to have thyroid alteration when he had serum TSH levels lower than normal range without exogenous T4 intake; a patient was considered to have an AT autoAb abnormality when he was positive for at least one AT autoAb. Missing observations were interpolated using data collected in the previous or subsequent month (where present), and only patients with complete observations after this interpolation were included. The only case with TSH above the normal range (a case of subclinical hypothyroidism) was not considered for this analysis, because it was already present at baseline and did not change status during treatment. GEE analysis, in fact, calculates probabilities of changing of status (from negative to positive, from normal to abnormal, and vice versa) of each serial observation compared with baseline. Two-sided descriptive P values are given as indicators of statistical significance.

Results

Demographic characteristics of the study groups

MS patients. The female to male ratio was 2:1; the age at study entry was 32.2 ± 6.5 yr (mean ± SD; range, 18–49); the age at disease onset was 21.6 ± 8.1 yr (range, 14–42); disease duration was 10.5 ± 5.4 yr (range, 2–27); the Expanded Disability Status Scale (23) score was 2.4 ± 1.2 (range, 1.5–3.5).

Healthy controls. The female to male ratio was 1:1.7; the age at entry was 42 ± 15.3 yr (range, 17–93).

Baseline comparison of thyroid function and autoimmunity with healthy normothyroidal controls (Table 1Go)

Baseline thyroid function evaluation of 152 of the 156 MS patients recruited was available. Two cases (1.3%) of clinically overt hyperthyroidism (1 AT autoAb positive), 2 patients with goiter (1.3%) and 3 with thyroid nodules (2%; all without thyroid function alterations), and 6 patients with a family history of thyroid disease (4%; all without thyroid function alteration, one anti-TMA autoAb positive) were excluded from the comparison with healthy normothyroidal controls. No cases below the lowest (0.1 mIU/liter) or above the highest (5 mIU/liter) TSH cut-off were found in MS patients. The risk of having a TSH level below 0.3 mIU/liter (OR, 0.84; CI, 0.32–2.19) or above 3.0 mIU/liter (OR, 0.37; CI, 0.05–3.01) was not significantly increased in MS patients. Adding anti-TMA autoAb positivity as an independent variable did not change the risk for MS patients of having a TSH level either below 0.3 mIU/liter (OR, 0.85; CI, 0.33–2.23) or above 3.0 mIU/liter (OR, 0.35; CI, 0.04–3.00). MS patients do not have an increased risk of having an abnormal TSH value even if they are anti-TMA autoAb positive. The frequency of subclinical hypothyroidism and that of anti-TMA autoAb positivity were slightly higher in MS patients, although not significantly so.

Longitudinal evaluation during IFNß treatment

Thyroid function alterations. No case of clinically overt hypothyroidism and 1 case of subclinical hypothyroidism was observed in the study. The latter was a man with subclinical hypothyroidism already present at baseline and persisting during treatment, with a transient subclinical worsening at months 6–9 (TSH increase from 3.7 to 6.3 mIU/liter). The patient was negative for AT autoAb both at baseline and during IFN treatment, and his hypothyroidism was the result of subacute thyroiditis. Two patients (of 152, 1.3%) at baseline had clinically overt hyperthyroidism, diffuse toxic goiter without AT autoAb, and toxic adenoma with anti-TMA and anti-TGA autoAb, respectively. Two patients (of 144, 1.4%) developed clinically overt hyperthyroidism de novo during IFNß treatment, in 1 case after 3 months of IFN treatment, returning to normothyroidal status by month 6 and after 12 months of treatment in the other. Both patients had subacute thyroiditis with low radioactive iodine uptake and were anti-TMA and anti-TGA autoAb negative during the entire study. A patient with subclinical hyperthyroidism at baseline developed clinically overt hyperthyroidism (toxic nodular goiter with high radioactive iodine uptake) at 3–6 months of treatment, returning to subclinical hyperthyroidism by the ninth month. He was AT autoAb negative during the entire study. Excluding the 2 cases with hyperthyroidism at baseline, 3 of 154 patients (1.9%) had clinical hyperthyroidism de novo during IFNß treatment, a figure not significantly different from that at baseline. No case of clinical hyperthyroidism de novo occurring during treatment was associated with AT autoAb positivity either at baseline or during treatment. The frequency of cases with TSH below the normal range (clinical hyperthyroidism included) was 5.3% at baseline (8 of 152 patients, in 1 case associated with anti-TMA and anti-TGA autoAb) and 8.3% de novo during IFNß treatment (12 of 144, in 1 case with anti-TGA autoAb at baseline, in another with anti-TMA autoAb de novo during treatment), without a statistically significant difference. The frequency of hyperthyroidism occurrence in each 3-month period during treatment pointed to random fluctuations throughout the study (Table 2Go), and GEE analysis showed that the probability of having a TSH level below the normal range at each time point analyzed during treatment was never significantly different from that at baseline (Table 3Go).


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Table 2. Occurrence of thyroid or liver function alteration or of antithyroid autoantibodies before and during interferon-ß treatment

 

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Table 3. Risk of thyroid or liver function alteration or of antithyroid autoantibody positivity at each 3-month interval during interferon-ß treatment compared to baseline: a generalized estimating equations analysis

 
Baseline thyroid function alteration persisted at least once during treatment in all cases (9 of 9, 100%) and at least twice in most (6 of 9, 67%). De novo occurring thyroid function alteration persisted in only 1 of 12 cases (8.3%), less frequently than alteration present at baseline (P = 0.005).

Thyroid function alteration in patients with baseline thyroid disease or a family history of thyroid disease (Table 4Go). The 2 cases of clinically overt hyperthyroidism persisted during treatment without worsening. The anti-TMA autoAb concentration increased (in the autoAb-positive case) from 145 to 331 IU/ml, and that of anti-TGA autoAb from 405 to 1102 IU/ml at months 3–6, then returned to values similar to baseline. The other patient remained AT autoAb negative for the entire study. Five patients had baseline thyroid disease (2 with goiters and 3 with thyroid nodules) without thyroid function alteration. One of the patients with goiter had de novo occurrence of anti-TGA autoAb at the third month of IFN treatment; the anti-TGA autoAb concentration progressively rose to 1335 IU/ml and persisted until the twelfth month; thyroid function, however, remained normal. The second patient with goiter developed transient clinical hyperthyroidism at the third month, which disappeared thereafter, and had no AT autoAb. Of the 3 patients with thyroid nodules, 2 developed transient subclinical hyperthyroidism, respectively, at the third and sixth to ninth months of IFN treatment, which disappeared thereafter; the latter remained normothyroidal. All 3 patients with thyroid nodules remained free of AT autoAb during the entire study. Five of the 6 patients with a family history of thyroid disease never had AT autoAb (either at baseline or during treatment), 3 remained normothyroidal, and 2 developed subclinical hyperthyroidism at the twelfth month of treatment. The remaining patient with a positive family history was baseline positive for anti-TMA autoAb. The autoAb concentration decreased below the positivity threshold by the twelfth month of treatment, and her thyroid function remained normal throughout the study. Comparing patients with and without goiter, thyroid nodules, or a family history of thyroid disease, 3 of 5 patients with and 9 of 139 patients without goiter or nodules developed hyperthyroidism during IFNß treatment (P < 0.001); 2 of 6 with and 10 of 138 without a family history of thyroid disease developed hyperthyroidism during treatment (P = 0.1). Patients with preexisting goiter or thyroid nodules seem to be at risk for developing transient thyroid dysfunction during IFNß treatment.


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Table 4. Thyroid function and autoimmunity during interferon-ß treatment in MS patients with baseline thyroid disease or a family history of thyroid disease

 
Liver function alteration. Liver function alteration occurred in 7 of 152 patients (4.6%) at baseline and in many more (57 of 152, 37.5%) de novo during IFNß treatment (Table 2Go). The frequency of liver alteration was definitely higher during treatment than at baseline (P < 0.0001). Most de novo cases of liver alteration occurred during the first 3-month interval (Table 2Go), and GEE analysis showed that the probability of having liver alteration changed significantly with time (Table 3Go). In particular, it was significantly higher (P <= 0.002) at the third and sixth months compared with baseline, returning to values no longer significantly different from baseline by the ninth month.

Baseline liver alteration persisted (in at least 2 determinations) during treatment in most cases (5 of 7, 71.4%). Liver alteration occurring de novo during IFNß treatment persisted in only 13 of 57 (22.8%) cases, less frequently than alteration present at baseline (P < 0.02).

Occurrence of AT autoAb. AT autoAb was detected in 15 of 149 patients (10.1%) at baseline and in 20 of 155 (12.9%) during IFNß treatment; anti-TMA autoAb was found in 11 of 149 (7.4%) at baseline and in 15 of 155 (9.7%) during treatment; anti-TGA autoAb was detected in 5 of 149 (3.3%) at baseline and in 9 of 155 (5.8%) during treatment. AT autoAb was detected de novo during treatment in 6 of 134 patients (4.5%; anti-TMA autoAb in 5 of 138, 3.6%; anti-TGA autoAb in 4 of 144, 2.8%), with random, nonsignificant frequency changes at each 3-month study period (Table 2Go). GEE analysis showed that the probability of having AT or anti-TMA autoAb positivity during IFNß treatment did not change significantly with time (Table 3Go).

Baseline AT autoAb positivity persisted (at least once during treatment) in most cases (13 of 15, 86.7%). AT autoAb positivity occurring de novo during IFNß treatment persisted in only 2 of 6 cases (33%), less frequently than autoAb positivity present at baseline (P < 0.05).

Correlation between AT autoAb positivity and thyroid function alteration (Table 5Go). De novo thyroid function alteration (clinically overt hyperthyroidism or TSH below the normal range) during IFNß occurred in 1 of the 15 patients with AT autoAb at baseline and in 11 (with 2 cases of clinical hyperthyroidism) of the 134 patients without AT autoAb at baseline ({chi}2 = 0.00; P = NS; Table 5Go). De novo thyroid function alteration occurred in 1 of the 6 patients with de novo AT autoAb and in 10 (with 2 cases of clinical hyperthyroidism) of the 134 who never had AT autoAb (neither at baseline or during IFNß; {chi}2 = 0.00; P = NS; Table 5Go). Statistical analysis did not show any significant correlation between the development of thyroid function alteration during IFNß treatment and AT autoAb positivity either at baseline (r = 0.047) or during treatment (r = 0.134).


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Table 5. Occurrence of clinical and subclinical thyroid function alteration during interferon treatment in MS patients stratified according to antithyroid autoantibody positivity

 
Discussion

Thyroid function alteration and autoimmunity have been reported in 2–10% patients treated with type I IFN (1, 2, 3, 4). They are considered contraindications to IFN treatment (1, 8), and frequent thyroid function assessments during IFN treatment are advised (1, 24, 25). Most reports describe patients treated with IFN{alpha} for chronic hepatitis C, a disease that seems to predispose to autoimmunity (6, 7). MS patients, too, may be predisposed to develop thyroid function alteration or autoimmunity during IFN treatment. The prevalence of thyroid dysfunction in MS patients ranges from 2–11%, and that of AT autoAb from 4–22% (26, 27, 28, 29, 30, 31) (Table 6Go). In some reports the prevalence is higher than that in the healthy control group, whereas in others it is not. Subjects positive for AT autoAb or with abnormal TSH level have an increased risk to develop thyroid dysfunctions (32, 33, 34), and some reports of thyroid dysfunction during IFNß treatment for MS (10, 11, 12, 13, 14) have, in fact, appeared. They are summarized in Table 7Go. The frequency of thyroid dysfunction during IFNß ranges from 1–13%, and that of AT autoAb ranges from 22–43%. Thyroid dysfunction and autoimmunity occur more often during first year of treatment (10, 12) and are almost always reversible (12). Anti-TMA autoAb is the AT autoAb most frequently studied in studies of MS patients as well as in those of patients treated with IFN{alpha} (1, 2, 3, 4). Anti-TMA and anti-TGA autoAb have been studied in powerful long-term epidemiological surveys (32, 33, 34), and anti-TMA autoAb positivity correlates well to the occurrence of thyroid dysfunction both in subjects free of any treatment (32, 35) as well as in those treated with IFN (5). Antithyroid peroxidase (anti-TPO) autoAb has been also studied in some reports dealing with MS patients (12, 13, 29). TPO is identical to or at least the major antigenic protein component of TMA (36), and lymphocytes producing anti-TMA autoAb also produce anti-TPO autoAb in patients with thyroid autoimmune disease (37).


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Table 6. Frequency of thyroid function alteration and of antithyroid autoantibody positivity in MS patients free of treatment

 

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Table 7. Frequency of thyroid function alteration and of anti-thyroid autoantibody positivity in MS patients during interferon beta treatment

 
Before starting IFNß treatment, we compared the frequency of thyroid dysfunction and AT autoAb positivity in our multicenter cohort of MS patients with that in a large group of healthy subjects collected from the blood banks of the same hospitals recruiting MS patients. The frequencies of both clinical and subclinical thyroid disease, of slight TSH level abnormalities, and of anti-TMA Ab positivity were not significantly increased in MS patients. We did not find any baseline thyroid function abnormality or antithyroid autoimmunity predisposing to thyroid dysfunction. We then followed up those patients during the first year of IFNß treatment. We observed only one case of subclinical hypothyroidism, already present at baseline, which persisted with a slight transient worsening during treatment. We monitored even subtle decreases in TSH below the normal range, as possible cases of initial subclinical hyperthyroidism. The frequency of cases with TSH below the normal range or with clinically overt hyperthyroidism did not significantly increase during IFNß treatment. Longitudinal analysis of frequency at baseline and at each 3-month period on treatment showed small changes, with a random distribution throughout the whole study period, without significant differences among different periods. Also, AT autoAb frequency did not significantly change from baseline during treatment. The absence of a clear-cut frequency change related to the beginning of IFNß treatment makes it difficult to correlate the occurrence of de novo cases of thyroid function alteration or autoimmunity to IFN treatment. On the other hand, longitudinal statistical analysis demonstrated a significantly increased probability of liver function alteration, in particular, during the first 3 months of IFNß treatment. Liver function alteration has been reported in 30–70% patients during type I IFN therapy (38, 39) and in 8–22% patients in clinical trials of IFNß in MS (40, 41, 42, 43). The significantly increased frequency of liver function alteration shortly after starting IFNß treatment is indirect evidence of a probable causal relationship.

The frequency of clinical or subclinical thyroid dysfunction during IFN{alpha} treatment ranges from 2.5–31% (1, 2, 3, 4), somewhat higher than that during IFNß treatment (ranging 1–13%) (10, 11, 12, 13, 14). IFN{alpha} binds to type I IFN-specific cell surface receptor with an affinity 1000-fold higher than that of IFNß (44) and has biological effects different from those of IFNß (45, 46). The frequency of AT autoAb is even more variable; it is reported in up to 70% of patients treated with IFN{alpha} (4) and in 22–43% of patients treated with IFNß (10, 11, 12, 13, 47, 48). Some reports showed an increased frequency of thyroid dysfunction or of AT autoAb during IFNß treatment compared with baseline, and others did not (Table 7Go). In our study the frequency of clinical and subclinical thyroid dysfunction during IFNß treatment was 8.3%; that of AT autoAb was 13%. The values are not significantly different from baseline frequency. All previous reports are cross-sectional studies of patient samples recruited in a single center and did not use a longitudinal statistical approach correcting for the correlation of repeated measurements of the same subject over time. Multicenter studies like ours reduce sampling bias due, for example, to ethnic or geographic origin, which is deemed important for thyroid dysfunction, and are more representative of the overall disease population. Therefore, the results of multicenter and single center studies may be different. The statistical approach we used (prospective, multicenter, with longitudinal analysis) demonstrated, during IFNß treatment, a significantly increased frequency of liver function alteration, but not of thyroid function or autoimmunity abnormalities. Most de novo alterations occurring during IFNß treatment (of liver or thyroid function as well as of autoAb positivity) were, eventually, transient, rarely persisting at the end of the year of follow-up. From the results of our analysis, there is no need for repeated assessment of thyroid function and autoimmunity in all MS patients treated with IFNß, probably only in those with preexisting thyroid autoimmunity, goiter, or thyroid nodules. Ongoing trials with IFNß in other diseases should further address this question with a thorough methodological approach.

Acknowledgments

The Betaferon Safety Trial study group includes M. Trojano and F. Giuliani (Clinica Neurologica, Bari); F. Salvi (Dipartimento di Scienze Neurologiche, Ospedale Bellaria, Bologna); S. Stecchi (Centro Sclerosi Multipla, Azienda USL Cittá di Bologna, Bologna); A. Reggio and E. Reggio (Clinica Neurologica, Catania); E. Montanari, G. Negri, and L. Ludovico (Divisione di Neurologia, Fidenza); A. Ghezzi and M. Zaffaroni (Divisione di Neurologia, Gallarate); G. L. Mancardi and M. Inglese (Clinica Neurologica, Genova); A. Carolei and R. Totaro (Clinica Neurologica, L’Aquila); C. Milanese and L. La Mantia (Divisione di Neurologia, Istituto Neurologico Besta, Milan); D.Caputo and M. Mini (Divisione di Neurologia, Istituto Don Gnocchi, Milan); R. Cotrufo and G. Lus (Clinica Neurologica, Naples); V. Cosi and A. Romani (Clinica Neurologica, Pavia); V. Gallai and P. Sarchielli (Clinica Neurologica, Perugia); U. Nocentini and B. Rizzato (Clinica Neurologica, Universitá Tor Vergata, Rome); P. A. Tonali and A. R. Massaro (Clinica Neurologica, Universitá Cattolica, Rome); G. Rosati and S. Sotgiu (Clinica Neurologica, Sassari); P. Annunziata (Clinica Neurologica, Siena); F. Bortolon and G. Stenta (Divisione di Neurologia, Vicenza); M. P. Sormani (Unitá di Epidemiologia Clinica e Trials, Istituto Nazionale per la Ricerca sul Cancro, Genova); K. Beckmann (Schering AG, Berlin, Germany); P. C. Brossa, E. Ghigo, and M. Maccario (Dipartimento di Medicina Interna, Universitá di Torino, Torino); F. Faggiano (Dipartimento di Sanitá Pubblica, Universitá di Torino); U. Ecari and M. Ciampini (Farmades, SpA, Rome). Coordinating center: Clinica Neurologica, Dipartimento di Neuroscienze, Universitá di Torino (Torino): L. Durelli, B. Ferrero, A. Oggero, E. Verdun, P. Barbero, A. Pipieri, A. Ricci, A. Bosio, M. A. Cucci, and B. Bergamasco. Coordinating center for laboratory investigations: Laboratorio Baldi e Riberi, Ospedale Maggiore S. Giovanni Battista (Torino): G. Aimo and L. Giorda.

Footnotes

This work was supported in part by Farmades, SpA (Rome, Italy).

Abbreviations: Ab, Antibody; AT, antithyroid; autoAb, autoantibodies; CI, confidence interval; fT3, free T3; fT4, free T4; GEE, generalized estimating equations; IFN, interferon; MS, multiple sclerosis; OR, odds ratio; TGA, autoAb against TG; TMA, autoAb against thyroid microsomal antigens; TPO, thyroid peroxidase.

Received December 17, 2000.

Accepted April 9, 2001.

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