Normal pressure hydrocephalus

Normal pressure hydrocephalus is characterised by the clinical features of hydrocephalus (i.e., levodopa-unresponsive gait apraxia with or without cognitive impairment or urinary symptoms), but without significantly raised cerebrospinal fluid pressure.

Cannot be reliably diagnosed using neuroimaging alone.

Differential diagnosis includes other causes of parkinsonism and common dementia disorders.

Responds to ventriculoperitoneal shunting if treated early enough.

Selection of patients for surgery is challenging as many are considered a high surgical risk.

Normal pressure hydrocephalus (NPH), also known as idiopathic normal pressure hydrocephalus (INPH), is a condition characterised by the clinical features of hydrocephalus (i.e., levodopa-unresponsive gait apraxia with or without urinary incontinence or cognitive impairment), but without significantly elevated cerebrospinal fluid (CSF) pressure as measured by lumbar puncture. Despite this, the condition responds to a reduction in CSF pressure and/or a CSF diversion procedure.[1]INPH Guidelines Study Group. Guidelines for the diagnosis and management of idiopathic normal pressure hydrocephalus. Neurosurgery. 2005;57(Suppl 3):S2-1-S2-52. https://academic.oup.com/neurosurgery/issue/57/suppl_3

NPH is a confusing and misleading term. The word 'hydrocephalus' is usually used to describe elevated CSF pressure in the brain. In NPH, there is no obvious build-up of CSF, and the pressure in the ventricular system of the brain is not considered significantly abnormal. Intracranial CSF pressure is slightly higher than normal, as CSF outflow resistance from the skull is relatively high.

Misdiagnosis or delayed diagnosis is common because: the criteria for diagnosis are variable and not very specific; diagnostic tests are of limited sensitivity; and in many patients with levodopa-unresponsive gait apraxia, the diagnosis is not considered. Because of this, some physicians doubt the existence of the condition.