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Clinical Studies |
Institutes of Endocrinology (M.M., A.P., G.B., L.M., L.C.) and Neurology (R.R., B.R., A.M.), University of Pisa, Pisa; and the Institute of Internal Medicine, University of Cagliari (S.M.), Cagliari, Italy; and the Division of Endocrinology and Metabolism, University of Massachusetts (L.E.B.), Worcester, Massachusetts 01655
Address all correspondence and requests for reprints to: Aldo Pinchera, M.D., Institute of Endocrinology, University of Pisa, Viale del Tirreno 64, 56018 Tirrenia-Pisa, Italy.
Myasthenia gravis (MG) may occur in association with autoimmune thyroid diseases (AITD). The aim of this study was to evaluate the features of MG associated with AITD compared to those of MG without AITD. A total of 129 MG patients (34 men and 95 women; age range, 11–81 yr) were subdivided into: group A, 56 MG patients with AITD [25 with autoimmune thyroiditis and 31 with Graves’ disease (GD)]; group B, 21 MG patients with nonautoimmune thyroid diseases; and group C, 52 MG patients without thyroid disease. The severity of MG was ranked according to the Osserman score. Laboratory evaluation included assays for antithyroid and antiacetylcholine receptor (AchRAb) antibodies.
Ocular MG (Osserman’s class 1) was more frequent in group A (41.0%)
than in group B (14.2%; P < 0.03) or C (21.4%;
P < 0.03). Severe generalized MG (classes 
2B)
was more frequent in groups B (57.1%; P < 0.03)
and C (51.9%; P < 0.02) than in group A (28.5%).
GD patients with clinical evidence of ophthalmopathy had a higher
frequency (P = 0.05) of ocular MG (57.8%) than GD
patients without clinical ophthalmopathy (16.6%). Thymic disease was
less frequent in group A (26.7%) than in group B (71.4%;
P = 0.001) or C (59.7%; P =
0.001). The prevalence of thymic hyperplasia was 17.8%, 38.0%, and
40.3% in groups A, B, and C, respectively; the prevalence of thymoma
was 8.9%, 33.4%, and 19.4%. When only patients with generalized MG
were considered, thymic disease was less frequent
(P < 0.02) in group A (40.6%) than in the
remaining groups (69.4%). AchRAb was more frequent in groups B
(57.1%) and C (57.6%; P < 0.03) than in group A
(35.7%).
In conclusion, MG associated with AITD has a mild clinical expression, with preferential ocular involvement and lower frequency of thymic disease and AchRAb. This supports the hypothesis that ocular and generalized MG are separate diseases with different spectra of associated diseases. Nonautoimmune thyroid diseases have no influence on the features of MG. The association of ocular MG and AITD might be due to a common autoimmune mechanism and/or a peculiar genetic background.
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