Neurophysiological changes in Japanese encephalitis

Japanese encephalitis (JE) is an encephalomyelitis involving cortex, subcortex, brainstem and spinal cord. There is paucity of studies on the neurophysiological evaluation in JE. This study aims at comprehensive evaluation of EEG, sensory and motor evoked potentials, nerve conduction and electromyography; and correlate these with clinical findings. Sixty five patients with JE diagnosed on the basis of clinical, radiological and virological criteria were subjected to a detailed clinical evaluation during the acute stage of illness. Cranial CT scan or MRI was carried out in all the patients. All the patients underwent 10 or 18 channel EEG, motor and sensory evoked potentials to both upper and lower limbs bilaterally as well as peroneal and sural nerve conductions and concentric needle EMG. Outcome, was defined at the end of 3 months into poor, partial and complete recovery. The patient's age ranged between 2-65 years. There were 40 males and 25 female patients. Fifteen patients were less than 12 years of age. History of seizure was present in 31 patients. Quadriplegia was seen in 39 and hemiplegia in 8 patients. Muscle wasting was present in 16 patients and tendon reflexes were reduced in 12 and of mixed pattern in 14 patients. Cranial MRI revealed thalamic lesion in 38, basal ganglia in 21, substantia nigra in 30, pons in 5, cerebellum in 3 and cerebral cortex in 7 patients out of 57 patients. EEG revealed nonspecific theta to delta slowing in 45, alpha pattern coma in 5 and epileptiform discharges in 8 patients. EMG revealed fibrillations in 23 patients. Motor evoked potentials were abnormal in 34 out of 46 patients and revealed patchy and focal abnormalities comprising of unrecordable, prolonged and normal pattern. Somatosensory evoked potentials were abnormal in 8 patients only. At 3 month, 26 patients had complete, 13 partial and 15 had poor outcome. Eight patients died in acute stage and 3 were lost to followup. MEP correlated with weakness and 3 month outcome whereas EEG, SEP and EMG did not have any correlation. MEP changes were more frequent in JE and had prognostic significance.