MSLT Booked After a Short Night and a Recent SSRI
Jordan, 20, is referred for PSG followed by MSLT after reporting sleep attacks, two episodes of knee buckling with laughter, and an ESS of 19. He took his last dose of sertraline 5 days ago and stopped it on his own. He kept no sleep diary and works rotating shifts. On the PSG, lights off at 22:30, sleep onset at 00:48, final awakening at 06:00, total sleep time 310 minutes, first REM period at 68 minutes. Five nap opportunities are scheduled at 2-hour intervals, the first at 08:00.
1. Is the MSLT valid as set up? Support your answer with the relevant standard.
Read the worked answer
No - the study does not meet the standard for a valid MSLT.
The MSLT is to be preceded by a PSG that documents total sleep time of at least 6 hours (360 minutes) on the patient's habitual sleep schedule. Jordan's TST is 310 minutes (5 h 10 min), 50 minutes short of the threshold. Sleep deprivation shortens mean sleep latency, which biases the test toward a false-positive narcolepsy result.
Two further problems:
- No 1–2 week sleep diary or actigraphy to establish habitual sleep and screen for insufficient sleep syndrome and shift-work disorder - both of which are on the differential and both of which can mimic the referral picture.
- The preceding night may not represent his habitual schedule at all.
Sleep onset at 00:48 after 22:30 lights-off is itself a red flag for a circadian or sleep-debt problem.
2. How does the sertraline affect interpretation, and what is your role regarding his medication?
Read the worked answer
Sertraline is REM-suppressing. An MSLT performed while REM suppression is active will under-detect SOREMPs, producing a false-negative for narcolepsy even in a patient who genuinely has it. A 5-day interval is not an adequate washout; roughly 2 weeks is the usual expectation for SSRIs (longer for fluoxetine).
Your role:
- Do not advise the patient to stop or restart medication. That is the prescriber's decision, made with the supervising physician.
- Report the medication history and the 5-day interval to the supervising physician before the naps begin.
- Note that a urine drug screen is typically part of the MSLT workup, and document the self-discontinuation.
Proceeding without flagging this converts a technically adequate test into a misleading one.
3. It is 07:40. What do you actually do, and what do you document?
Read the worked answer
Do not simply run the five naps and let the data be interpreted as definitive.
Actions:
- Notify the supervising physician before 08:00 - TST 310 min, sertraline stopped 5 days ago, no diary or actigraphy, rotating shifts.
- Follow the physician's direction: the realistic options are to cancel/reschedule the MSLT after documented adequate sleep and an appropriate washout, or to proceed with an explicit note that the result is conditional.
- Prepare the patient for the possibility of a repeat study; explain why rather than letting him think he failed.
Document:
- PSG TST 310 min, lights off/on, sleep onset, REM latency 68 min.
- Medication history and timing of self-discontinuation.
- Absence of sleep diary/actigraphy and the rotating-shift work pattern.
- The time you notified the physician, the name, the response, and the patient's understanding of the plan.