Endocrine Abstracts

Introduction: Myasthenia gravis (MG) is a chronic neuromuscular condition characterized by weakness in voluntary muscles. It is an autoimmune disorder. The emergence of the condition can be abrupt. As with any autoimmune disease (AID), it may be associated with other AIDs. We report a case of MG associated with Hashimoto’s thyroiditis (HT).

Observation: The diagnosis of MG was established in a 58-year-old patient, based on the progressive onset of fatigue, excessive salivation, difficulty in chewing, and ptosis. Electromyography revealed signs indicative of neuromuscular junction involvement. Anti-acetylcholine receptor antibodies were positive. The patient was prescribed Pyridostigmine (Mestinon®) and showed a good response to treatment. The diagnosis of MG was made 3 months before identifying profound hypothyroidism, which was incidentally discovered during the investigation of other autoimmune diseases. The hypothyroidism was attributed to HT, confirmed by positive anti-thyroid peroxidase antibodies and anti-thyroglobulin antibodies. The patient received treatment with L-thyroxine for the thyroid disorder. The clinical and biological outcomes were favorable, achieving euthyroidism.

Discussion/Conclusion: The diagnosis of MG is based on the clinical presentation - often starting with ocular symptoms such as ptosis or diplopia, extending to other muscles in 80% of cases, worsening with exertion, and characterized by episodic progression -, the response to anticholinesterase medications, the detection of anti-acetylcholine receptor antibodies, and the presence of a decrement in electromyography. MG can be associated with numerous autoimmune thyroid diseases (AITDs), especially autoimmune thyroiditis. The underlying pathophysiological basis connecting these conditions is not clearly established, but an immunological cross-reaction between the neuromuscular junction and thyroid components has been identified in both MG and AITD, such as autoimmune thyroiditis. The prevalence of AITD among individuals with MG is generally higher than that in the general population. In fact, 9% of men and 18% of women with MG exhibit autoimmune thyroid diseases. These diseases are predominantly characterized by hyperthyroidism (17.5%), simple goiter (1.7%), or more rarely, hypothyroidism (0.4-0.7%).

References: 1. Amin S, Aung M, Gandhi FR, Pena Escobar JA, Gulraiz A, Malik BH. Myasthenia Gravis and its Association With Thyroid Diseases. Cureus. 2020 Sep 4;12(9):e10248.

2. Mohamed N, Mohd Zin F, Mohd Yusoff SS. An association of myasthenia gravis with Hashimoto’s thyroiditis in a patient with a multinodular goitre. Malays Fam Physician. 2017 Aug 31;12(2):29-3