Mixed Upper and Lower Motor Neuron Damage in Japanese Encephalitis Virus Infection

Cerebral manifestations in Japanese B encephalitis are well known. However, there are very few studies focusing on extra-cerebral manifestations, among which focal anterior horn cell involvement is exceedingly rare. We herein report a case of Japanese B encephalitis with focal anterior horn cell involvement and unfurl how stepwise clinical approach and targeted investigations helped to solve the diagnostic conundrum. A 27-year-old female was admitted with fever, headache, altered sensorium, and convulsions. She tested positive for Japanese B encephalitis-IgM. Following conservative management, she regained consciousness after 5 days when neurological examination revealed marked cognitive impairment, medial convergence of eyeballs, upward gaze restriction, upper limbs dystonia with brisk tendon jerks, and flaccid paraparesis. A repeat neurological examination, on day 15 of admission, showed marked wasting and intermittent fasciculation in both lower limbs. Brain magnetic resonance imaging showed asymmetrical (right > left) bilateral thalamic and midbrain lesions, hyperintense on T2 and T2-fluid-attenuated inversion recovery (FLAIR)-weighted imaging with mild diffusion restriction on diffusion-weighted imaging and apparent diffusion coefficient map, suggestive of encephalitis. Nerve conduction study revealed decreased compound muscle action potentials exclusively in lower limbs with intact sensory nerve action potentials. Electromyogram showed chronic denervation potentials and presence of spontaneous activity in lower limbs, but not in upper limbs, indicative of focal anterior horn cell involvement. Prognosis of Japanese B encephalitis does not only depend on cerebral sequelae. Anterior horn cell involvement can dictate poor outcome and can easily be missed if not carefully dealt with.