A 23 year old man presents to his GP with episodes of leg weakness following bouts of laughing...

A 23-year-old man presents to his GP. He describes episodes of leg weakness following bouts of laughing whilst out with friends. The following weekend his friends described a brief collapse following a similar episode.

What is the most likely diagnosis?
A. Stokes-Adams attack
B. Cataplexy
C. Hypokalaemic periodic paralysis
D. Absence seizure
E. Myasthenia gravis

Answer: B. Cataplexy

Discussion

Cataplexy describes the sudden and transient loss of muscular tone caused by strong emotion (e.g. laughter, being frightened). Around two-thirds of patients with narcolepsy have cataplexy.

Cataplexy without narcolepsy is rare and the cause is unknown.


Features range from buckling knees to collapse.Attacks are brief, most lasting from a few seconds to a couple of minutes, and typically involve dropping of the jaw, neck weakness, and/or buckling of the knees. Even in a full-blown collapse, people are usually able to avoid injury because they learn to notice the feeling of the cataplectic attack approaching and the fall is usually slow and progressive

As cataplexy is a neurological problem, it can be misdiagnosed as a seizure disorder.

There is no cure for cataplexy, but it can be managed with medications and modification of potential triggers.