Pupillometry to differentiate idiopathic hypersomnia from narcolepsy type 1

Area of Science:

• Neuroscience
• Ophthalmology
• Sleep Medicine

Background:

• Idiopathic hypersomnia (IH) diagnosis lacks specific biomarkers, complicating differentiation from other central hypersomnias.
• Light significantly regulates sleep-wake cycles, involving the melanopsin-based non-visual pathway.
• Pupil response to light, mediated by melanopsin, offers a potential objective measure for sleep disorders.

Purpose of the Study:

• To investigate melanopsin-based pupil responses in patients with idiopathic hypersomnia (IH) and narcolepsy type 1 (NT1).
• To assess the utility of pupillometry in distinguishing between IH and NT1.

Main Methods:

• Pupillometry was used to measure pupil diameter and the relative post-illumination pupil response (PIPR) in 36 IH patients, 27 NT1 patients, and 43 healthy controls.
• Logistic regression analyses, adjusted for age and sex, were employed to compare groups.
• The diagnostic accuracy of basal pupil size for differentiating IH from NT1 was evaluated.

Main Results:

• Both IH and NT1 groups showed a significantly reduced PIPR compared to controls, indicating impaired melanopsin-mediated responses.
• NT1 patients exhibited a smaller baseline pupil diameter than both IH patients and controls.
• Basal pupil size effectively discriminated between IH and NT1, with a sensitivity of 72.22% and specificity of 66.67%.

Conclusions:

• Melanopsin-mediated pupil responses are diminished in both idiopathic hypersomnia and narcolepsy type 1.
• Baseline pupil diameter serves as a distinguishing feature between IH and NT1.
• Pupillometry offers a promising tool for the multi-feature differentiation of central hypersomnia subtypes.