Simultaneous Diagnosis of Myasthenia Gravis and Neurosyphilis, With Symptoms Improving After Neurosyphilis Treatment: A Case Report.

Simultaneous diagnosis of myasthenia gravis (MG) and early asymptomatic neurosyphilis is extremely rare. There have only been two cases described in the literature. To the best of our knowledge, this was the first case of MG resolving with concurrent treatment of neurosyphilis. Our patient was a 67-year-old male who presented to the hospital with a diffuse rash, bilateral ptosis, bilateral facial weakness, and bulbar symptoms (dysarthria, difficulty with mastication, and difficulty drinking fluids).  After testing positive for syphilis in serum and cerebrospinal fluid (CSF), the patient was diagnosed with neurosyphilis. Thus, it was suspected that his neurological findings were manifestations of early symptomatic neurosyphilis. The patient was treated with intravenous penicillin G for one week, and later, it was switched to intravenous ceftriaxone for two weeks due to cost and convenience. All symptoms resolved after three to four weeks. After being discharged, the patient tested positive for acetylcholine receptor antibodies. Subsequently, the patient underwent an electromyogram (EMG), which revealed a decremental response, confirming a diagnosis of MG. Infections are known to trigger autoimmune diseases and can lead to the development of new-onset MG. Neurosyphilis is relatively highly associated with other central nervous system (CNS) antibodies and can trigger other neurological disorders. Recognizing the differences in presentation and performing an accurate and comprehensive neurological exam can help differentiate early symptomatic neurosyphilis from neuromuscular disorders such as MG.