Balamuthia Mandrillaris Amoebic Encephalitis Clinically Mimicking as Myasthenia Gravis Exacerbation: A Diagnostic Challenge

The case is a 70-year-old immunocompromised male with a history of myasthenia gravis (MG). He presented with new-onset, persistent diplopia and headache unresponsive to prior therapy, initially suspected to be a recurrent MG exacerbation, for which oral prednisone was added to his treatment. The patient's condition worsened over the 10-day period following the clinic visit, with ongoing vision loss, increasing weakness, and intermittent shortness of breath. During this period, he also experienced a transient episode of right-hand numbness, which resolved spontaneously. He was admitted for suspected recurrent MG; neurology raised concerns about an alternative underlying process and ordered a magnetic resonance imaging (MRI) scan, which revealed multiple ring-enhancing lesions highly suggestive of an intracranial infection. Empiric antibiotics were initiated, but an extensive infectious disease workup was inconclusive. He was discharged in stable condition, with a brain biopsy and follow-up MRI scheduled for further evaluation. Five days later, he returned to the emergency department with decreased level of consciousness, fever, and confusion. He underwent a brain biopsy, which revealed evidence of an amoebic infection. In the subsequent days, his condition deteriorated rapidly, and he passed away on the same day that a diagnosis of Balamuthia mandrillaris infection was confirmed via PCR on a brain tissue sample. This case highlights significant diagnostic challenge in MG patients, where rare infections can closely mimic disease flare-ups. As demonstrated in our case, failing to recognize infections can lead to severe consequences. In MG patients with worsening, treatment-resistant symptoms and atypical presentations, MRI is strongly recommended.