Dropped head syndrome as the sole presenting manifestation of probable post-cytomegalovirus immune-mediated brainstem encephalitis in an immunocompetent woman: a case report.

Background: Dropped head syndrome (DHS) is a rare, disabling chin-on-chest deformity caused by severe cervical extensor weakness. The etiologic spectrum is dominated by peripheral myopathies, motor neuron disease, and myasthenia gravis; central nervous system causes are seldom considered, particularly in older adults where coexisting cervical spondylosis appears to offer a unifying structural explanation. To our knowledge, DHS as the sole presenting manifestation of brainstem encephalitis has not been previously reported. Case presentation: A 60-year-old immunocompetent woman presented with four months of progressive cervical kyphosis beginning two weeks after a self-limited upper respiratory illness. Initial orthopedic evaluation attributed her posture to degenerative cervical disease, but the structural findings did not account for the severity of selective neck-extensor weakness. Multidisciplinary reassessment disclosed bilaterally absent gag reflexes and rightward tongue deviation, cranial-nerve signs that localized dysfunction to the medulla. Lumbar puncture showed mildly elevated protein (0.73 g/L) and a distinctive intrathecal immunoglobulin pattern, with markedly elevated IgA and IgM and mildly elevated IgG. CSF was positive for cytomegalovirus (CMV)-specific IgG alone among the TORCH antigens tested, despite serum positivity for CMV, herpes simplex virus type 1, and rubella; CMV DNA by PCR was negative. Paired quantitative titres yielded a CSF antibody-specific index of approximately 10, consistent with intrathecal CMV-specific antibody synthesis. Contrast-enhanced (gadobutrol) and STIR craniocervical MRI, together with brain MRI, showed no abnormal cord or brainstem enhancement or acute signal abnormality. Competing etiologies-structural cervical disease, primary and hypothyroid myopathy, CNS tuberculosis, and paraneoplastic syndrome-were systematically excluded. A 14-day course of moderate-dose corticosteroids, combined with cervical orthosis and structured rehabilitation, produced complete resolution. Remission was sustained at one-year follow-up; surgery was avoided. Conclusions: DHS can be the sole presenting manifestation of probable post-CMV immune-mediated brainstem encephalitis, even when brain MRI is unrevealing and cervical degeneration appears to provide a structural explanation. Careful cranial-nerve examination, CSF immunological profiling with intrathecal immunoglobulin quantification, and multidisciplinary reassessment are essential for distinguishing central from peripheral DHS. In this patient, moderate-dose corticosteroids produced complete recovery even when initiated well outside the conventional early treatment window, and potentially obviated cervical surgery.