What is CSF tap test?

The CSF tap test, sometimes lumbar tap test or Miller Fisher Test, is a medical test that is used to decide whether shunting of cerebrospinal fluid would be helpful in a patient with suspected normal pressure hydrocephalus. The test involves removing 30 mL of cerebrospinal fluid through a lumbar puncture, after which cognitive function is clinically reassessed. The name "Fisher test" is after C. Miller Fisher, a Canadian neurologist working in Boston, Massachusetts, who described the test.

Clinical improvement showed a high predictive value for subsequent success with shunting. 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.