Rare Case of Late-onset Myasthenia Gravis in a 65-year-old Female with Prolonged Doxycycline Use

Myasthenia gravis (MG) is a rare autoimmune condition caused by antibody-mediated disruption of acetylcholine receptors (AChR) or their associated proteins. The age of onset of MG has a bimodal distribution, with a predominance of female cases in the second and third decades and a predominance of male cases in the sixth to eighth decades. MG is often unmasked by stressors such as systemic illness, medication, surgery, and pregnancy. We present a case of late-onset MG in a 65-year-old female with a recent history of prolonged doxycycline use. However, there are aspects of her past medical history, including comorbidities involving the immune system and numerous drug intolerances that should have increased clinical suspicion for MG. Additionally, one medical event that preceded symptom onset was pneumonia treated with doxycycline. This case suggests that doxycycline should be used with caution in MG patients, and that MG should be considered as part of the differential diagnosis in older female patients presenting with neurologic symptoms and suggestive past medical history.