Prevalence of idiopathic normal pressure hydrocephalus in patients with degenerative cervical myelopathy

Degenerative cervical myelopathy (DCM) and idiopathic normal pressure hydrocephalus (iNPH) share symptoms such as gait disturbance and urinary dysfunction, especially in the elderly. While the incidence of DCM in patients with iNPH is reported, the prevalence of iNPH in patients with DCM remains unclear. This study investigates the prevalence of iNPH in DCM patients.

This retrospective cohort study included 83 patients undergoing decompression surgery for DCM between April 2018 and March 2023. Brain MRI performed within three years prior to surgery was analyzed. Patients were categorized into two groups based on the Evans Index (EI): those with EI > 0.3 were classified as the Suspected-iNPH group, and those with EI ≤ 0.3 as the Non-iNPH group. Pre- and postoperative Japanese Orthopedic Association (JOA) scores and Patient-Reported Outcomes (PROs), including the Neck Disability Index (NDI), EuroQOL-5D (EQ-5D), Core Outcome Measure Index (COMI), and Numerical Rating Scale (NRS) for pain, were compared. Suspected-iNPH cases underwent further analysis to identify disproportionately enlarged subarachnoid space hydrocephalus (DESH).

Thirty-one patients (37%) were classified as Suspected-iNPH, who were significantly older (p = 0.01). No significant differences were found in pre- or postoperative JOA scores, and PROs. DESH was identified in 6 patients (7%), with 2 diagnosed as probable-iNPH based on cerebrospinal fluid tap tests.

A notable proportion of elderly DCM patients exhibit ventricular enlargement and DESH, suggesting a potential overlap with iNPH. Brain MRI should be considered for elderly DCM patients, particularly when neurological symptoms deviate from typical patterns.