High prevalence of cervical myelopathy in patients with idiopathic normal pressure hydrocephalus

Background: Both idiopathic normal pressure hydrocephalus (iNPH) and cervical myelopathy may result in progressive gait impairment. Some patients who do not respond to shunting despite a positive tap test may have gait dysfunction from cervical myelopathy. The objective of this study was to determine the prevalence of cervical myelopathy in patients with iNPH. Methods: A consecutive series of patients undergoing shunt placement for iNPH were screened for cervical stenosis. Clinical manifestations of iNPH and cervical myelopathy, grade of cervical stenosis, cervical spine surgical intervention, timing of intervention, and outcomes were recorded. Results: Fifty-two patients shunted for treatment of iNPH were included for analysis. 58 % were male with a mean age of 75.2 years (SD 7.3 years). All patients presented with gait disturbances. 39/52 (75 %) had cervical stenosis, and 9/52 (17.3 %) had significant (grade 2 - 3) cervical stenosis with myelopathy and were subsequently treated with surgical decompression. There was an association between increasing grade of stenosis and disproportionately enlarged subarachnoid space hydrocephalus (DESH). All patients with grade 2 - 3 cervical stenosis and symptoms of cervical myelopathy in addition to iNPH underwent cervical decompression surgery. Conclusions: Clinically significant cervical myelopathy was prevalent in patients with iNPH and was associated with increased rate of DESH, a finding that requires validation in a larger cohort. Based on these results, cervical imaging could be considered preoperatively in patients with iNPH, particularly when upper motor neuron findings are identified. Additionally, concomitant cervical stenosis should be ruled out in patients whose gait does not improve after shunt placement.