Occurrence of subdural hematoma and resolution of gait disturbance in a patient treated with shunting for normal pressure hydrocephalus

A 66-year-old man with gait disturbance was diagnosed with normal pressure hydrocephalus (NPH) and treated with ventriculoperitoneal shunting using a programmable valve. The valve ultimately set at a pressure of 40 mmH₂O after higher settings no longer relieved symptoms. However, this pressure setting was excessively low and was associated with occurrence of bilateral subdural hematomas. Paradoxically, this event was associated with stable improvement of gait. Our patient's gait disturbance was unassociated with muscle weakness, spasticity, cerebellar ataxia, or Romberg's sign, and, therefore, was consistent with a frontal gait disorder. Cerebral cortical blood flow as measured after shunting by single photon emission computed tomography (SPECT) was slightly increased from the value before shunting, possibly because of intracranial hypotension related to the valve setting. Lasting improvement of gait in our case may be a result of increased blood flow in the supplementary motor area (SMA).