Fundoscopy as a diagnostic biomarker in idiopathic normal pressure hydrocephalus: a pilot study

Idiopathic normal pressure hydrocephalus (iNPH) has a prevalence of approximately 5%. It is characterised by Hakim's triad of impaired gait, cognitive dysfunction and urinary incontinence. Despite radiological markers and liquor-dynamic tests, iNPH is difficult to diagnose due to many overlapping symptoms. The aim of this study was to evaluate funduscopy as a noninvasive method of screening patients with suspected iNPH.

Patients with suspected iNPH who underwent a lumbar infusion test (LIT) were included. Funduscopy was performed before the start of the LIT, and intracranial pressure (ICP) was continually measured via lumbar cannulation. Retinal images were analysed using an artificial intelligence algorithm to determine the arteriole-venule (A/V) ratio. The A/V ratio and ICP measurements were compared with the iNPH diagnosis. In addition, the mean difference in shunt response was evaluated.

A significantly lower mean A/V ratio was found in the iNPH group compared with the non-iNPH group (p value: 0.02). Receiver operating characteristic curve analysis with an area under the curve of 0.75 showed a sensitivity of 88% and a specificity of 50% with an A/V cut-off of 0.86. Although not statistically significant, the mean A/V ratio was lower in the group with clinical shunt effect compared with those without (p value: 0.305).

This study found a statistically significant difference in baseline A/V ratios between iNPH and non-iNPH groups. This pilot study suggests the A/V ratio might be able to serve as a screening tool for iNPH. If so, this would be highly beneficial for patients and could have significant medical and socioeconomic implications.