Normal Pressure Hydrocephalus (NPH) is a condition in which the patient has dilated ventricles because of excessive cerebrospinal fluid, yet is able to maintain a normal opening pressure during a lumbar puncture. It occurs most commonly in elderly patients (> 60 years of age).
NPH may be idiopathic or secondary to conditions that impair CSF absorption (traumas, subarachnoid hemorrhage, and infections such as chronic meningitis)
SIGNS & SYMPTOMS:
The disease is characterized by the insidious onset of the triad:
– Ataxia (gait and balance disorders)
– Incontinence (mild to severe urinary incontinence)
– Dementia (mild to severe changes in cognition and behavior)
Complete history and physical examination should be obtained, as well as other tests that are useful when evaluating dementias, such as B12 levels and TSH.
MRI is the best imaging method and may show ventriculomegaly with normal sulcal sizes. Loss of signal in the aqueduct of Silvius (aqueduct flow void) may be present, as well as white matter lesions. The presence of cortical atrophy, however, may point to a different cause of dementia (such as AD).
Mini–Mental State Examination may be used to access the degree of cognition impairment. Neuropsychological testing, however, is probably better and allows the establishment of a baseline functional status, providing better basis for future monitoring of therapeutic response.
Lumbar puncture to remove CSF (tap test or lumbar drain) is useful and the improvement of symptoms may be used as a predictor of success for the surgical intervention.
Even though not routinely recommended, hydrodynamic studies with CSF infusion may be used to determine CSF outflow resistance and pressure volume index.
Intracranial pressure monitoring may also be used and can reveal intermittent rhythmic pressure deviations (Lundberg B waves – 0.5-2/min oscillations). The presence of B waves and basal ICP greater than 5-10mmHg may be helpful to establish the diagnosis of NPH.
Since there is no definitive method for diagnosis, a combination of different methods should be used before definitive treatment. A suggestion would include:
- Compatible history & physical
- Suggestive MRI
- A test that shows improvement after CSF drainage (such as lumbar tap)
- Absence of significant comorbidities or poor response predictors (see below).
Ventricular shunting (ventriculoperitoneal or ventriculoatrial) is the treatment of choice for NPH. However, not all patients respond well to the treatment.
Patients in which the gait disturbance appears earlier and it is more prominent tend to respond better to shunting.
Patients that may respond poorly to shunting include the ones with:
– Advanced dementia
– Long duration of symptoms (>2 years).
– Idiopathic NPH
SOURCES & FURTHER READING:
- Tsakanikas D, Relkin N. Normal Pressure Hydrocephalus. Semin Neurol 2007; 27(1): 058-065.
- Gallia GL et al. The diagnosis and treatment of idiopathic normal pressure hydrocephalus. Nature Clinical Practice Neurology (2005) 2, 375-381.
- Halperin JJ et al. Practice guideline: Idiopathic normal pressure hydrocephalus: Response to shunting and predictors of response. Neurology December 8, 2015 vol. 85 no. 23 2063-2071.