Longitudinal extensive transverse myelitis is an exceedingly rare condition with several known triggering factors, both viral and bacterial. While it has been widely associated with COVID-19, it can also occur following pneumonia caused by other agents. The underlying mechanism can include aquaporin-4 antibodies (AQP4-Ab). It causes major neurological manifestations and poses a life-threatening risk, particularly by affecting respiratory muscles. This case report delineates longitudinal extensive transverse myelitis following unilateral pneumonia, associated with AQP4-Ab, in a 62-year-old woman who experienced abdominal pain, a gradual loss of sensation in the extremities, and eventual inability to walk with a total loss of sensation. Her spinal MRI revealed increased T2 signal, consistent with longitudinal extensive transverse myelitis. AQP4-ab antibodies were present. Treatment with methylprednisolone led to symptom improvement. Protein levels in the cerebrospinal fluid were also analyzed. Our findings suggest a potential difference in protein levels in cerebrospinal fluid between bacterial and viral longitudinal extensive transverse myelitis. Magnetic resonance imaging is the primary method of diagnosis and can help exclude other possible etiologies of neurological symptoms. When managing longitudinal extensive transverse myelitis, timing is critical to prevent paralysis of the respiratory muscles. Although extremely rare, longitudinal extensive transverse myelitis can have diverse origins as well as clinical manifestations, and its management continues to present a significant challenge.