3665 Seronegative autoimmune encephalomyelitis with area postrema symptoms

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We present a case of seronegative autoimmune encephalomyelitis in an Australian patient who developed encephalopathy, intractable hiccups, and extensive myelitis. MRI demonstrated longitudinally extensive spinal cord involvement and area postrema abnormalities. Cerebrospinal fluid (CSF) analysis revealed an inflammatory profile but tested negative for aquaporin-4 (AQP4), myelin oligodendrocyte glycoprotein (MOG), and glial fibrillary acidic protein (GFAP) antibodies. The patient’s partial response to corticosteroids and plasma exchange, despite initial empirical treatment for infectious encephalitis, suggested an autoimmune mechanism. A subsequent post-plasma exchange serum sample detected weakly positive GFAP IgG, though pre-exchange CSF testing remained negative.Given the distinctive clinical and radiological features, we propose that tanycytes, specialised ependymal cells within the area postrema, may be an alternative immune target. Like astrocytes, tanycytes express GFAP and are strategically located in circumventricular organs, where immune-mediated interactions could contribute to encephalomyelitis pathogenesis. Their role in CSF-blood exchange and neuroendocrine regulation may explain the area postrema symptoms observed.This case underscores the diagnostic challenges posed by seronegative autoimmune encephalomyelitis and highlights the need for further investigation into glial targets beyond GFAP. Expanding the scope of autoantibody screening may enhance our understanding of tanycyte-associated neuroinflammation in such disorders.

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