Rabies viral encephalitis: clinical determinants in diagnosis with special reference to paralytic form

Background Rabies is an important public health problem in developing countries such as India where an alarmingly high incidence of the infection is reported every year despite the availability of highly effective, potent and safe vaccines. In clinical practice, diagnosis of the furious (encephalitic) form of rabies poses little difficulty. In contrast, the paralytic form poses a diagnostic dilemma, to distinguish it from Guillain–Barré syndrome. The problem is further compounded in the absence of a history of dog bite, clinical features resembling a psychiatric syndrome. Method The present study analysed the spectrum of neurological manifestations in 47 cases of rabies encephalitis (34 paralytic, six encephalitic, and seven psychiatric manifestations) from two hospitals in south India, confirmed at post-mortem by demonstration of a viral antigen in the brain. A history of dog bite was elicited in 33 patients and fox bite in one. Twenty-two patients received postexposure prophylaxis. The incubation period ranged from 7 days to 4 years. Clinical features were analysed, looking for any clinical pointers that provide clues to a diagnosis of paralytic rabies. Results and discussion Fever, distal paresthaesias, fasciculation, alteration in sensorium, rapid progression of symptoms and pleocytosis in cerebrospinal fluid should alert the neurologist to consider rabies encephalomyelitis. Detection of the viral antigen in the corneal smear and a skin biopsy from the nape of the neck had limited usefulness in the ante-mortem diagnosis. Although a few clinical signs may help indicate rabies encephalomyelitis antemortem, confirmation requires neuropathological/neurovirological assistance. The preponderance of atypical/paralytic cases in this series suggests that neurologists and psychiatrists need to have a high index of clinical suspicion, particularly in the absence of a history of dog bite.