Brainstem Encephalitis With Conflicting Autoimmune and Infectious Markers: A Case Report

The differential diagnosis of inflammatory diseases of the central nervous system has a very wide spectrum, and the diseases may mimic one another. Although modern techniques help clinicians make a final diagnosis, there still can be challenges and pitfalls in some cases. We present an 18-year-old female patient who presented with signs of brainstem encephalitis, which was accompanied by a small hyperintense lesion in the frontal lobe. The radiological findings were nonspecific, and her cerebrospinal fluid findings were normal. However, she had positive centromere antibody in the serum and positive CD45 antibody in the minor salivary gland biopsy. These markers led to the initial diagnosis of a rheumatological disorder, vasculitis, and immunosuppressive treatment was started. However, in the following weeks, her condition got worse. Further investigations showed positivity on the interferon-g release assay test. This changed the diagnosis to tuberculosis, advancing under immunosuppressive treatment. Despite the given antituberculosis treatment, the lesion in the frontal lobe eventually progressed and became eligible for biopsy, while the lesion in the brainstem was stable. The biopsy showed the lesion in the frontal lobe as "astroblastoma." The brainstem lesion started to recover after the removal of the tumor, and it was diagnosed as a paraneoplastic complication of the malignancy. This case showed how the differential diagnosis can be challenging and that the markers can sometimes be misleading. We would like to present the case for its educational value and its rarity.