Scattered reports exist describing secondary narcolepsy that develops following disease or organic insult to the brain. The present study is concerned with one particular type of secondary narcolepsy, posttraumatic narcolepsy, which we define as "narcolepsy that develops following a head injury in a previously asymptomatic individual". We obtained data on nine patients who had been previously diagnosed with mild to moderate closed head injury and who had unresolved sleep complaints. All patients presented with complaints of excessive daytime somnolence and/or sleep attacks. Patients also presented with a mix of cataplexy, hypnagogic hallucinations and/or sleep paralysis. All patients had undergone previous neurological and/or neuropsychological evaluation and testing, with seven of the nine patients having the Halstead-Reitan Neuropsychological Test Battery. Human leucocyte antigen (HLA) tissue typing was obtained in six of the nine cases. The standard protocol was utilized, consisting of overnight polysomnography with a Multiple Sleep Latency Test (MSLT) the following day. All patients' histories were negative for narcolepsy or any other significant sleep disorders prior to the head injury. The results of the neuropsychological testing indicated that all patients fell within the mild to moderate impairment range. The results of overnight polysomnography and MSLT data, along with patient histories, indicated a diagnosis of narcolepsy in all cases. The results of HLA typing indicated that three patients were DR2 positive, two were DR4 positive and one was DQW1 positive. We conclude that narcolepsy may be "dormant" and that, in cases genetically at risk, even a minor injury to the central nervous system can cause that person to become symptomatic.
