Rabies Encephalitis and the Use of Optic Nerve Sheath Diameter to Detect Elevated Intracranial Pressure

Rabies is a rare but rapidly progressive and almost universally fatal disease. A previously healthy 59-year-old male presented with rabies encephalitis. We measured his optic nerve sheath diameter (ONSD) daily in both eyes using ultrasonography to indirectly monitor for elevated intracranial pressure (ICP). We performed CT and MRI brain on days when his ONSD changed significantly. An increase in ONSD temporally correlated with radiologic findings of cerebral edema and acute subarachnoid hemorrhage (SAH). ONSD measurement is a fast, inexpensive, and widely-available imaging modality that may serve as a surrogate marker for elevated ICP. It may be especially useful in patients who are difficult to be transported to radiology due to the unstable nature of their disease.