somnography/MSLT should be performed after the individual is no longer taking any
psychotropic drugs and after re gular sleep-wake patterns, with out shift work or sleep de-
privation, have been documented.
A sleep-onset REM period during the poly somnography (REM sleep latency less than
or equal to 15 minutes) is highly specific (a pproximately 1% positive in control subjects)
but moderately sensitive (approximately 50%). A positive MSLT  result displays an aver-
age sleep latency of less than or equal to 8 minutes, and sleep-onset REM periods in two or
more naps on a four- or five-nap test. The MS LT result is positive in 90%–95% of individ-
uals with narcolepsy versus 2%–4% of control subjects or individuals with other sleep dis-
orders. Additional polysomnographic findings often include frequent  arousals, decreased
sleep efficiency, and increased stage 1 sleep.  Periodic limb moveme nts (found in about
40% of individuals with narcolepsy) and sleep apnea are often noted.
Hypocretin deficiency is demonstrated by  measuring CSF hypocretin-1 immunoreac-
tivity. The test is particular ly useful in individuals with suspected conversion disorder
and those without typical cataplexy, or in treatment-refractory cases. The diagnostic value
of the test is not affected by medications, sleep deprivation, or circadian time, but the find-
ings are uninterpretable when the individual is severely ill with a concurrent infection or
head trauma or is comatose. CSF cytology, protein, and glucose are within normal range
even when sampled within weeks of rapid onse t. CSF hypocretin-1 in these incipient cases