Cataplexy with Normal Sleep Studies and Normal CSF Hypocretin: An Explanation?

Area of Science:

• Neurology
• Sleep Medicine
• Neuroscience

Background:

• Narcolepsy diagnosis typically involves excessive daytime sleepiness (EDS) and cataplexy.
• Low cerebrospinal fluid (CSF) hypocretin-1 levels are a common biomarker for narcolepsy.
• Cataplexy usually occurs with or after the onset of EDS.

Observation:

• A patient presented with isolated cataplexy, a rare initial symptom.
• Multiple sleep latency tests (MSLT) were initially non-diagnostic.
• Cerebrospinal fluid (CSF) hypocretin-1 levels were initially normal (217 pg/mL).

Findings:

• The patient subsequently developed EDS.
• Repeat CSF analysis revealed significantly decreased hypocretin-1 levels (< 110 pg/mL).
• This suggests a delayed development of narcolepsy biomarkers.

Implications:

• This case expands the understanding of narcolepsy's varied clinical presentation.
• It underscores the importance of longitudinal monitoring in suspected narcolepsy cases.
• Highlights that normal hypocretin-1 levels do not always exclude narcolepsy, especially in early stages.