IIH with normal CSF pressures?

Idiopathic intracranial hypertension (IIH) is a condition of raised intracranial pressure (ICP) in the absence of space occupying lesions. ICP is usually measured by lumbar puncture and a cerebrospinal fluid (CSF) pressure above 250 mm H2O is one of the diagnostic criteria of IIH. Recently, we have encountered two patients who complained of headaches and exhibited disc swelling without an increased ICP. We prescribed acetazolamide and followed both patients frequently; because of the definite disc swelling with IIH related symptoms. Symptoms and signs resolved in both patients after they started taking acetazolamide. It is generally known that an elevated ICP, as measured by lumbar puncture, is the most important diagnostic sign of IIH. However, these cases caution even when CSF pressure is within the normal range, that suspicion should be raised when a patient has papilledema with related symptoms, since untreated papilledema may cause progressive and irreversible visual loss.