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

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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.