When to apply this diagnosis

• EDS with impairment but features are atypical—mixed features, unusual age‑onset, or partial symptom clusters.
• Incomplete or conflicting diagnostic testing (PSG/MSLT) where the clinician documents a clear reason for the “other specified” label.
• Useful as a working diagnosis to guide initial management and expedite specialist referral while further evaluation proceeds.

Atypical presentations covered

• Long‑sleeping patients with unrefreshing naps but MSLT without sleep‑onset REM periods and without clear idiopathic narcolepsy features.
• EDS with circadian misalignment patterns that do not fit a defined circadian rhythm disorder.
• Mixed pictures where obstructive sleep apnoea or periodic limb movements coexist with hypersomnolence and objective testing is confounded.
• Late‑onset hypersomnolence without classic narcoleptic features in middle‑aged or older adults where neurodegenerative causes are being considered.

Assessment priorities

1. Comprehensive sleep history: sleep timing, nap behaviour, sleep inertia, automatic behaviours, bed partner reports.
2. Medication and substance review—identify sedating agents, opioids, benzodiazepines, antihistamines and recent changes.
3. Screen for coexisting sleep disorders: screening questionnaires for OSA, RLS and insomnia; consider overnight oximetry or PSG where indicated.
4. Consider neurocognitive testing and neurological examination if late onset or progressive features suggest encephalopathy or neurodegenerative disease.

Investigations & interpretation tips

• Polysomnography (PSG) to exclude sleep‑disordered breathing and significant periodic limb movements; ensure adequate sleep opportunity before MSLT.
• MSLT helpful but interpretation requires stable sleep schedule and medication washout; borderline results may justify the “other specified” label while repeating testing or pursuing alternate assessments.
• Actigraphy over 1–2 weeks to document sleep–wake patterns and excessive time in bed (hypersomnia due to insufficient sleep syndrome can mimic hypersomnolence).
• Investigations for medical causes: thyroid function, full blood count, liver/renal function, and where indicated, neuroimaging or lumbar puncture if inflammatory/neurological disease suspected.

Management — practical clinical steps

1. Address reversible contributors: treat OSA, optimise medication regimens, manage depression and metabolic causes.
2. Behavioural strategies: sleep scheduling, strategic short naps, light therapy for circadian alignment and activity structuring.
3. Pharmacologic therapy: consider wake‑promoting agents when impairment persists—modafinil/armodafinil are commonly used; solriamfetol, pitolisant or traditional stimulants may be considered via specialist input in refractory cases.
4. Safety and occupational advice: counsel regarding driving, heavy machinery and consider workplace adjustments until symptoms controlled.

Specialist referral indications

• Unclear or conflicting PSG/MSLT results, suspected narcolepsy features (cataplexy, sleep paralysis, hypnagogic hallucinations).
• Late‑onset or rapidly progressive hypersomnolence where neurological causes are possible.
• Failure to respond to first‑line wake‑promoting agents or concern about stimulant misuse/side effects.

Key clinical points

• “Other specified” is a pragmatic label used when EDS is impairing but the presentation or testing is atypical or confounded.
• Exclude reversible causes, ensure adequate objective testing where possible, and consider wake‑promoting therapy with specialist input when appropriate.
• Prioritise safety (driving, occupation), repeat assessments when needed and refer to sleep medicine for complex or refractory cases.