Dementia and gait disorder are the most conspicuous and early signs of normal-pressure hydrocephalus. Given the potential for successful treatment, it is imperative to distinguish other conditions simulating the clinical picture of normal-pressure hydrocephalus. The most common cause of dementia is Alzheimer disease. Gait in Alzheimer disease is usually unremarkable until the late stages of the illness. Enlarged ventricles can be also found in Alzheimer disease because of brain atrophy (hydrocephalus ex vacuo). The degree of cortical atrophy in hydrocephalus ex vacuo is usually disproportionally more advanced than in patients with normal-pressure hydrocephalus. Thus, prominent early gait disorder with relatively short history of dementia in a patient with enlarged ventricles may be more suggestive of normal-pressure hydrocephalus than of Alzheimer disease. Patients with coexisting normal-pressure hydrocephalus and Alzheimer disease, confirmed by brain biopsy, have diminished postoperative improvement of normal-pressure hydrocephalus symptoms (Hamilton et al 2010). The overlap of normal-pressure hydrocephalus and Alzheimer disease may be common, and one study found the coexistence of these 2 entities in 89% (8 of 9 cases) (Cabral et al 2011).
Another common type of dementia is dementia with Lewy bodies. This needs to be considered in patients with fluctuating cognitive impairment, visual hallucinations, and mild extrapyramidal features with shuffling gait. Neuroimaging is usually diagnostic in differentiating normal-pressure hydrocephalus and dementia with Lewy bodies.
Multiinfarct dementia and Binswanger disease can have similar clinical manifestations, but MRI or CT usually detects signs of multiple strokes. Features seen in multiinfarct dementia not characteristic of normal-pressure hydrocephalus include high Hachinski ischemia scale score, presence of multiple infarctions on CT or MRI, focal neurologic deficit, and history of stroke. The presence of associated disease causing gait changes (osteoarthritis or spinal canal stenosis) may obscure normal-pressure hydrocephalus, and these patients should be followed closely for progression and appearance of cognitive deficits. Vascular pathology may be also very common in patients with normal-pressure hydrocephalus (Leinonen et al 2012).
Patients with Parkinson disease also have hypokinetic gaits with a reduced gait velocity and highly variable stride length. Broad-based gait with outward rotated feet and diminished height of the steps can help differentiate normal-pressure hydrocephalus from Parkinson disease. Moreover, the gait of patients with normal-pressure hydrocephalus does not improve with external cues that are beneficial in patients with Parkinson disease (Stolze et al 2001). Baseline postural instability of patients with suspected normal-pressure hydrocephalus suggests an alternative diagnosis and, if shunted, their outcome tends to be poor (Klassen and Ahlskog 2011). Other causes of gait difficulties simulating normal-pressure hydrocephalus (eg, spinocerebellar degenerations or cerebellar degeneration due to chronic alcoholism) have more ataxic character (Fisher 1982). Congenital hydrocephalus may become symptomatic with aging and may mimic normal-pressure hydrocephalus. Head circumference at or greater than the 98th percentile suggests congenital etiology. Thus, head circumference measurement should be part of an examination in suspected normal-pressure hydrocephalus. Furthermore, patients with normal-pressure hydrocephalus had bigger head circumference when compared with normal sex-matched and age-matched controls. This suggests that a considerable fraction of these patients actually have a congenital hydrocephalus that became symptomatic in late adulthood (Krefft et al 2004).