Is Normal Pressure Hydrocephalus a Valid Concept in 2002?
September 1, 2002 4 minutes read
Abstract & Commentary
Source: Bret P, et al. Is normal pressure hydrocephalus a valid concept in 2002? A reappraisal in five questions and proposal for a new designation of the syndrome as "chronic hydrocephalus." J Neurol Neurosurg Psychiatry. 2002; 73:9-12.
1. Was NPH actually a newly discovered condition when reported by Adams, Fisher, and Hakim in 1965?
The answer is no. In 1936, Riddoch published a paper called, "Progressive dementia without headaches or changes in the optic discs due to tumors of the third ventricle" (Brain. 1936;59:225-233). In 1956, Foltz and Ward published a paper called "Communicating hydrocephalus from subarachnoid bleeding" (J Neurosurg. 1956;13:546-566) and McHugh also published a paper called "Occult hydrocephalus" (Q J Med. 1964;33:297-312). Both these latter papers were published in or adjacent to my department in Seattle. Nevertheless, the definitive characterization which brought the syndrome to clinical attention was the report of Adams et al in 1965, and they were the first to show the efficacy of shunting.
2. Is CSF pressure really normal in patients with NPH?
The actual readings of CSF are often moderately and physiologically high because of anxious muscle tension in the patient. Then, with the needle remaining in place, the patient relaxes and CSF fluid pressure drops 15-20 mm of CSF with the patient supine and the manometer erect. It can be argued, however, that a single CSF measurement by lumbar puncture may not adequately reflect the true intracranial pressure, or the presence of numerous B waves.
3. Is NPH really a cause of curable dementia?
Bret wisely says "no" to this question. He states bluntly, "patients with NPH do not fit the criteria of degenerative (Alzheimer-type) or arteriosclerotic dementia." This is largely a semantic argument. Most neurologists accept the premise that NPH is a cause of curable dementia, particularly if strict criteria are used in establishing the diagnosis. As pointed out by Bret and colleagues this criteria includes:
• Presence of a clearly identified etiology;
• Predominant gait difficulties with mild or absent cognitive impairment;
• Substantial improvement after CSF withdrawal (CSF tap test);
• Normal sized or occluded sylvian fissures and cortical sulci on CT or MRI;
• Absent or moderate white matter lesions on MRI.
4. Is NPH specific to the adult and elderly population?
This section deals with pediatric cranial malformations, which may produce a syndrome in children analogous to that of NPH in adults with subtle mental deterioration, gait abnormalities, and delayed bladder control.
5. Is CSF diversion the only treatment modality?
Ventriculoperitoneal shunts have become standard treatments although ventriculoatrial shunts are still a second-line treatment. Lumboperitoneal shunts have never gained widespread acceptance in the treatment of patients with NPH, probably because they are strictly limited to communicating forms of hydrocephalus. Whatever the type of shunt, the major nuisance is the high rate of complications. Thus far, only truly satisfactory ventricular drainage is effective. Third ventriculostomy in patients with aqueductal stenosis may be effective but only a few patients and their surgeons have experience with this technique.
Conclusion
Bret concludes his commentary with a number of points.
A. Some carefully selected patients respond to shunting which remains the standard today. Nevertheless, complications are high, although newer programmable shunts eliminate some of the difficulties.
B. Presently, the term "normal pressure hydrocephalus NPH" is an oxymoron, indicating a static illness. The problem lies that in reality NPH is likely to be a dynamic process that gradually and insidiously disrupts the intracranial structures.
C. It has become obvious that the other elements of the historical concept of NPH need to be revised. NPH should not be regarded as an age-related disease specific to the adult and elderly population. A similar condition may be encountered during childhood, with a clinical presentation that does not differ basically from that of the adult and may be erroneously ascribed to "arrested hydrocephalus," which is a distinct condition. More important, the term NPH is questionable because it matches neither the real conditions nor the current diagnosis. This is established in most institutions on the basis of the clinical and CT presentation only, without assessment of the ICP nor the actual CSF manometric profile of such patients. This is acknowledged by the results of dynamic tests that showed a general trend to increased, albeit compensated, pressure levels or at least an inability of compensatory mechanisms to dampen a sudden increase of ICP in patients with NPH.
Bret proposes a more relevant nosographic designation for the NPH syndrome by renaming it "chronic hydrocephalus" without reference to age and CSF pressure. Although this proposal is attractive, it is unlikely to be adopted after many decades of neurologists being taught that NPH is one of the rare treatable causes of dementia. NPH is an active process that results from failure of the resorptive mechanisms of the CSF. It may be regarded as an intermediate state of balance between uncompensated hypertensive hydrocephalus and asymptomatic hydrocephalus (in which compensatory systems are fully effective). As proved by follow-up monitoring of shunted patients, insertion of a shunt in those suffering from chronic hydrocephalus often provides a clinical cure without changes in their ventricular size. Shunting may, therefore, be regarded as an additional compensatory system allowing chronic hydrocephalus in turn to become asymptomatic hydrocephalus, which may be the only condition that really deserves the label NPH. What is truly needed to revolutionize the treatment of NPH is improved means of identifying patients who will respond to shunts. The initial results at New York Presbyterian Hospital—Weill Cornell Medical College suggest that this may be possible using sophisticated new MRI imaging techniques. —Fred Plum
Dr. Plum, Professor and Chairman, Department of Neurology and Neuroscience, Weill-Cornell Medical College, is Editor of Neurology Alert.
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