378 Sleep-Wake Disorders
sity, especially when the narcolepsy is untreated. Rapid weight gain is common in young
children with a sudden disease onset. Comorbid sleep apnea sh ould be considered if there
is a sudden aggravation of preexisting narcolepsy.
Relationship to Internat ional Classification of 
Sleep Disorders
The International Classificat ion of Sleep Disorders,  2nd Edition (ICSD-2), differentiates five
subtypes of narcolepsy.
Breathing-Related Sleep Disorders
The breathing-related sleep disorders category encompasses three relatively distinct dis-
orders: obstructive sleep apnea hypopnea, ce ntral sleep apnea, an d sleep-related hypo-
ventilation. 
Obstructive Sleep Apnea Hypopnea
Diagnostic Criteria 327.23 (G47.33)
A. Either (1) or (2): 
1. Evidence by polysomnography of at least five obstructive apneas or hypopneas per
hour of sleep and either of the following sleep symptoms:
a. Nocturnal breathing disturbances: snor ing, snorting/gasping, or breathing
pauses during sleep.
b. Daytime sleepiness, fatigue, or unrefreshing sleep despite sufficient opportuni-
ties to sleep that is not better explained by another mental disorder (including a
sleep disorder) and is not attribut able to another medical condition.
2. Evidence by polysomnography of 15 or more obstructive apneas and/or hypopneas
per hour of sleep regardless of accompanying symptoms.
Specify current severity:
Mild:  Apnea hypopnea index is less than 15.
Moderate: Apnea hypopnea index is 15–30.
Severe:  Apnea hypopnea index is greater than 30.
Specifiers