374 Sleep-Wake Disorders
lepsy with cataplexy but withou t hypocretin deficiency, test  results for human leukocyte
antigen (HLA) DQB1*06:02 may be negative. Seiz ures, falls of other origin, and conversion
disorder (functional neurological symptom disorder) should be excluded. In narcolepsy
secondary to infectious (e.g., Whipple’s dise ase, sarcoidosis), traumatic, or tumoral de-
struction of hypocretin neuron s, test results for HLA DQB1* 06:02 may be positive and may
result from the insult triggeri ng the autoimmune process. In other cases, the destruction of
hypocretin neurons may be secondary to trau ma or hypothalamic surgery. Head trauma
or infections of the central nervous system can, however, produce tran sitory decreases in
CSF hypocretin-1 levels without hypocret in cell loss, complicating the diagnosis.
Diagnostic Features
The essential features of sleepiness in narcolep sy are recurrent daytime naps or lapses into
sleep. Sleepiness typica lly occurs daily but must occur at a minimum three times a week
for at least 3 months (Criterion A). Narcolep sy generally produces cataplexy, which most
commonly presents as brief episodes (seconds to minutes) of sudden, bilateral loss of mus-
cle tone precipitated by emotions, typically  laughing and joking. Muscles affected may
include those of the neck, jaw, arms, legs, or  whole body, resulting in head bobbing, jaw
dropping, or complete falls. Individuals are awake and aware during cataplexy. To meet
Criterion B1(a), cataplexy must be triggered by  laughter or joking and must occur at least
a few times per month when the condition is untreated or in the past.