Recognising CADASIL in adults with NPH-like syndrome.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a NOTCH3-related small vessel disease that can mimic idiopathic normal pressure hydrocephalus (iNPH). A woman in her late 70s presented with the classic iNPH triad: progressive gait disturbance with falls, urinary incontinence and cognitive decline. Brain MRI showed ventriculomegaly with periventricular hyperintensities and a narrow callosal angle (60°), supporting iNPH, but also revealed non-confluent white matter hyperintensities in the anterior temporal poles and external capsules; features strongly suggestive of CADASIL. A large-volume cerebrospinal fluid tap test produced no objective gait improvement. Family history disclosed a relative with similar gait/psychiatric illness and poor outcomes after shunting. Genetic testing confirmed a heterozygous pathogenic NOTCH3 variant, establishing CADASIL. This case underscores that 'NPH-compatible' imaging and a normal pressure hydrocephalus-like syndrome do not confirm iNPH; clinicians should consider CADASIL when tap test is negative and MRI/family history suggests small vessel vasculopathy.