Human Herpesvirus 6 (HHV-6)-Associated Longitudinally Extensive Transverse Myelitis Preceded by Mycoplasma pneumoniae Infection in an Immunocompetent Adult: A Report of a Unique Case

In immunocompetent individuals, human herpesvirus 6 (HHV-6) is an uncommon cause of severe neurological illness. We describe the case of a 38-year-old man who had previously been in good health. He initially presented with fever and cough, followed by abrupt flaccid paraparesis, a T10 sensory level, and urinary retention. Neurological examination showed extensor plantar responses, hyperreflexia, and bilateral lower limb weakness. Magnetic resonance imaging of the spine demonstrated longitudinally extensive transverse myelitis (LETM) from T1 to T10. <i>Mycoplasma pneumoniae</i> was detected on initial serologic testing. The diagnosis of HHV-6 meningomyelitis was confirmed by lumbar puncture, which showed lymphocytic-predominant pleocytosis and a positive HHV-6 PCR result in the CSF. High-dose intravenous corticosteroids, azithromycin, and intravenous ganciclovir were administered, leading to successful treatment with notable neurological improvement and the ability to walk with assistance at discharge. This case highlights the diagnostic challenges of HHV-6, an emerging pathogen that can cause serious CNS complications such as LETM in immunocompetent hosts. It also raises the possibility of a combined immunomodulatory and antiviral therapeutic approach, even in the presence of a concurrent infection.