Unmasking NMOSD: A Case of Misdiagnosed Ethambutol-Induced Optic Neuropathy
Background:
Neuromyelitis Optica Spectrum Disorder (NMOSD) is a rare autoimmune condition often misdiagnosed due to its clinical overlap with other disorders. This report elucidates the diagnostic challenges in a 57-year-old female initially misdiagnosed with ethambutol-induced optic neuropathy.
Design/Methods:
Case report
Results:
A 57-year-old white female with a history of COPD, pulmonary embolism, and a cavitary lesion in the right upper lung lobe presented with subacute left-sided vision loss. This impairment arose after the initiation of triple therapy with rifampin, azithromycin, and ethambutol for her nontuberculous Mycobacterium kansasii infection. MRI scans highlighted a pronounced diffuse enhancement, mainly in the left optic nerve, extending mildly to the chiasm and the proximal right optic nerve, indicative of optic neuritis. Initially, the left-sided visual disturbance and relative afferent pupillary defect were thought to be side effects of ethambutol, prompting its discontinuation. However, even after ceasing ethambutol, she completely lacked vision in the left eye. About a month following the onset of the left-sided visual changes, she developed a right-sided temporal hemianopsia. Fortunately, it improved after a week-long course of intravenous corticosteroids, leading to the complete restoration of vision in her right eye. Sadly, the corticosteroid regimen and plasma exchange interventions had no restorative effect on her left eye's vision, leaving her with substantial disability. Intriguingly, while her age is atypical for NMOSD, she tested positive for aquaporin-4 antibodies on two distinct occasions & CSF analysis detected oligoclonal bands, affirming the NMOSD diagnosis. Furthermore, a comprehensive chart review unveiled chronic mild hyponatremia, a condition known to be linked with NMOSD due to SIADH.
Conclusions:
This case highlights the intricacies involved in diagnosing NMOSD, especially in individuals with multiple coexisting health issues. It underscores the necessity of an all-encompassing diagnostic approach, incorporating specific laboratory and imaging assessments, to ensure precise diagnosis and appropriate therapeutic interventions.