Co-existence of Myasthenia Gravis and Addison's Disease Without Thymoma: A Case Report

Myasthenia Gravis (MG) and Addison's Disease (AD) co-existing is very rare. The estimated prevalence of this co-occurrence is less than 1 in 100 000, underscoring its clinical significance. We present a female case with coexisting AD and MG. A 45-year-old female arrived at our clinic complaining of breathing difficulties for a month, a drooping left eyelid, and swallowing difficulties for 10 days. She has been treated with 5 mg/day prednisone for AD for three years. Long-term corticosteroid therapy may modulate immune responses and influence the timing of MG onset. Neurological evaluation revealed partial ptosis in the left eye and mild tetraparesis (4/5 strength).

Cortisol level was 0.8 µg/dL, and adrenocorticotropic hormone (ACTH) level was 987 ng/L, an adrenal crisis was excluded. The anti-acetylcholine receptor antibody (anti-AChR antibody) level was 8.37 nmol/L (> 0.4 nmol/L). Repetitive nerve stimulation, neostigmine, and Simpson tests were compatible with MG. Therefore, she was diagnosed with MG.

Acetylcholine antibodies in MG may indicate that other autoimmune diseases may be added to the clinic in these patients. Keeping in mind the presence of the underlying MG may be life-saving for those who do not react well to therapy or in the case of newly added findings in AD patients.