Pneumomediastinum – Uncommon presentation of Rabies
A 17-year-old male from tribal area of northern Kerala was brought to the emergency department with complaints of breathlessness, agitated behaviour of one day duration. He was in his usual good health, prior to the onset of symptoms.
At the time of admission patient was conscious, oriented and anxious. On neurological examination, Glasgow Coma Scale was (15/15).Plain Computed Tomography (CT) of head showed air in the retropharyngeal space extending between C1-C4 vertebral body levels(figure1), a finding picked up incidentally prompted us to review the chest radiograph and history.The lateral scout image of skull with neck showed air in the retropharyngeal space extending between C1-C4 vertebral body levels.Axial CT sections of skull base in bone window settings showed air involving the deep neck spaces spanning retropharyngeal, parapharyngeal, carotid and posterior cervical space (figure 3)On reviewing the frontal chest radiograph, there was streaky air lucencies outlining soft tissues of lower neck bilaterally, extending down along the mediastinum, with band of air lucency lifting the mediastinal pleura laterally on the left side and outlining and lifting the thymic remnant (figure 4)History was reviewed. He had history of stray dog bite to his left index finger about two and a half months back;
The pneumomediastinum is diagnosed in 1/44,500 of accident and emergency attendances or 1/100,000 of natural birthsThis rare condition is confirmed via chest X-ray or CT scanning of the thorax. Severe central chest pain is the most common symptomThe basic pathophysiology of pneumomediastinum and interstitial air leak in rabies still remains elusive, however un-self-controlled, violent spasm of pharynx and the larynx resulting in acute and transit obstruction of airway and the oesophageal lumen, can cause alveolar or oesophagus rupture under a transient high pressure. Boerhaaves syndrome has been reported in rabiesRabies is a highly fatal zoonotic viral disease (3) caused by neurotropic RNA virus of genus Lyssavirus, family Rhabdoviridae.The disease is invariably fatal for humans, in the absence of post exposure prophylaxis prior to the onset of symptoms. Broadly based on clinical manifestation rabies can be classified into classic furious and atypical paralytic type. The furious type has dramatic clinical presentation in the form of aerophobia, hydrophobia, hypersalivation and aggressive behaviour, and often easily diagnosed even in the absence of clinical history of exposureNevertheless, the paralytic form most often has atypical clinical presentation or complication leading to delayed detection and misdiagnosisHence imaging in rabies is seldom done, with imaging findings in rabies encephalitis showing nonspecific areas of hypoattenuation in the basal ganglia, hippocampus, brainstem, and periventricular white matter, and late cases showing diffuse cerebral swelling and haemorrhage.
Rabies, though best known with catastrophic clinical manifestation, uncommon presentation like pneumomediastinum or extensive subcutaneous emphysema, should prompt the clinician to have index of suspicion to prevent misdiagnosis or delay in diagnosis of the atypical presentation of rabies.