Miller Fisher test

The Miller Fisher test is a diagnostic procedure used to confirm suspected normal pressure hydrocephalus (NPH). The Miller Fisher test confirms NPH if the removal of 30 mL of cerebrospinal fluid (CSF) results in clinical improvement of NPH symptoms.

Diagnosis of NPH is usually first led by a lumbar puncture, followed by the evaluation of clinical response to removal of CSF. This can be followed by a CT, MRI, and continuous external lumbar CSF drainage during 3 or 4 days.

Lumbar puncture is usually the first step in diagnosis of NPH and the opening pressure measured carefully. In most cases, CSF pressure is usually above 155 mmH₂O. Clinical improvement after removal of CSF (30 mL or more) has a high predictive value for subsequent success with shunting. This is called the "lumbar tap test" or "Miller Fisher test". A "negative" test has a very low predictive accuracy, as many patients may improve after a shunt in spite of lack of improvement after CSF removal.

History

Described by neurologist, Charles Miller Fisher.