When Gastroenteritis Struck the Brain: Post-infectious Parkinsonism Suggestive of Neuropsychiatric Systemic Lupus Erythematosus in a Patient With Aqueductal Stenosis.

Parkinsonism is a rare neuropsychiatric manifestation of systemic lupus erythematosus (SLE), the pathogenesis of which has been proposed to involve immune-mediated vasculopathy. Gastrointestinal infections may exacerbate autoimmune responses, triggering disease flares. We present a 26-year-old woman who developed acute parkinsonism with mutism, oromandibular dystonia, and horizontal square wave jerks following a diarrheal illness. Neurological examination revealed cogwheel rigidity and dysphagia. Brain MRI showed periventricular hyperintensities, ventricular dilation, and aqueductal stenosis without basal ganglia infarcts or lesions. Antinuclear antibody was positive (1:100) with anti-SS-A and anti-SS-B antibodies, while complement levels remained within normal limits. Treatment with pulsed methylprednisolone, rituximab, hydroxychloroquine, and levodopa-carbidopa resulted in marked neurological improvement. The patient did not fulfill the 2019 European League Against Rheumatism/American College of Rheumatology classification criteria for SLE; however, the clinical features and robust therapeutic response were consistent with a presumptive diagnosis of neuropsychiatric SLE presenting as parkinsonism. This case underscores the importance of considering SLE in young patients with atypical parkinsonism, particularly following a gastrointestinal illness. It highlights that complement levels may not reliably reflect disease activity in all patients.