The gait disturbance that accompanies NPH may be of several different types, as discussed in Chap. 6. These are difficult to classify and only vaguely simulate the patterns observed in Parkinson disease or cerebellar ataxia, but certain features predominate. Most often, there is unsteadiness and impairment of balance and shortening of the step length, with the greatest difficulty being encountered on stairs and curbs (Fisher, 1982). Weakness and tiredness of the legs are frequent complaints, although examination discloses no paresis or ataxia. An impression of Parkinson disease may be conveyed, with short steps and slightly stooped, forward-leaning posture, but the resemblance is superficial because there is typically no shuffling, nor is there festination, rigidity, slowness of alternating movement, or tremor. Some patients present with unexplained falls, often helplessly backward, but on casual inspection the gait may betray little abnormality except a minimal reduction in step length and overall slowness. When the condition remains untreated, the steps become shorter, with more frequent shuffling and falls; eventually standing and sitting and even turning over in bed become impossible. Fisher referred to this advanced state as “hydrocephalic astasia–abasia.”
The mental changes in the cases we have encountered have been, broadly speaking, “frontal” in character and embodied mainly apathy, dullness in thinking and actions, and slight inattention. Memory trouble is eventually a component of the overall problem and has been predominant in some cases, for which reason the diagnosis of Alzheimer disease is sometimes considered before the discovery of hydrocephalus, but as a rule, the gait derangement of NPH is fairly obvious by the time memory function is substantially impaired. There is usually a degree of affective indifference, but the patient reports little in the way of emotionality. Patients who display gait difficulty with prominent and progressive verbal, graphical, and calculation difficulties are more likely to have a degenerative or cerebrovascular disease. In those cases, the difficulty with walking and stability is ostensibly a result of frontal lobe disease, either degenerative or infarctive, as discussed in Chap. 6. Unfortunately, beyond the above-noted defects that are elicitable by routine testing, we have not found neuropsychologic tests of great value in the diagnosis of NPH.
Urinary symptoms appear relatively later in the illness. Initially, they consist of urinary urgency and frequency. Later, the urgency is associated with incontinence, and ultimately there is frontal lobe incontinence,” in which the patient is indifferent to his lapses of continence, and bowel control becomes similarly disordered.
The cause of the syndrome of NPH in most cases cannot be established and on weak grounds, asymptomatic fibrosing meningitis is often presumed to have been present. An uncertain proportion of cases can be traced to congenital aqueductal stenosis that has allowed normal brain function into adulthood and, for unknown reasons, decompensates; a few of our patients have become symptomatic after mild head trauma. This is probably the most common imputed cause of the syndrome but again, on uncertain grounds. An identical syndrome may follow subarachnoid hemorrhage from ruptured aneurysm, resolved acute meningitis or a chronic meningitis (tubercular, fungal, syphilitic, or other), Paget disease of the base of the skull, mucopolysaccharidosis of the meninges, and achondroplasia.
That the mechanical effect of ventricular enlargement on the adjacent brain is responsible for the syndrome is supported by Fisher’s observations (2002) that a reduction in ventricular size caused by extrinsic compression from subdural collections has been associated with clinical improvement. One presumes that the main clinical features are due to dysfunction of the frontal lobes and their connections with the striatum, from mechanical pressure or distortion, but this is conjecture.
Diagnosis of NPH