[Utility of acute-phase cerebral blood flow single photon emission computed tomography (SPECT) for evaluating the...

Bickerstaff's brainstem encephalitis (BBE) is an autoimmune disorder typically localized to the brainstem. While cortical involvement is rare, severe cases presenting with decorticate posturing and profound consciousness disturbance can mask typical clinical features, making early diagnosis challenging. A 22-year-old woman developed progressive numbness in her limbs and lips, visual impairment, and impaired consciousness 13 days after an episode of gastroenteritis. Upon admission, she exhibited a Japan Coma Scale score of III-200, decorticate posturing, absent brainstem reflexes, and hyperreflexia. Cerebrospinal fluid analysis revealed pleocytosis and elevated protein levels. Although contrast-enhanced MRI showed only faint enhancement along the leptomeninges of the cerebral cortex and midbrain, acute-phase ¹²³I-IMP cerebral blood flow (CBF) single photon emission computed tomography (SPECT) demonstrated diffuse cortical hypoperfusion and paradoxical hyperperfusion in the bilateral basal ganglia. Furthermore, multiple autoantibodies associated with autoimmune encephalitis and demyelinating diseases-including anti-NMDAR, LGI1, CASPR2, AMPAR, GABABR, DPPX, GlyR, mGluR5, MOG, and AQP4 antibodies-were all negative in both serum and cerebrospinal fluid. Following aggressive immunotherapy, her consciousness improved rapidly. It was only during this recovery phase that the classic BBE triad of total ophthalmoplegia and ataxia became apparent, which had been masked by the initial severe consciousness disturbance. The diagnosis of BBE was retrospectively confirmed based on this clinical evolution and the high titers of serum anti-GQ1b and anti-GT1a IgG antibodies. Follow-up SPECT confirmed the normalization of CBF, correlating with her clinical recovery. This case demonstrates that cerebral perfusion SPECT is capable of detecting reversible dysfunction within the cortex and basal ganglia in BBE. It highlights the importance of considering BBE even in atypical cases with predominant cortical symptoms, where the diagnosis may only become clear through clinical evolution and ancillary functional imaging.