- Note that these studies were published as abstracts and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
- Several studies suggest that narcolepsy is associated with a significantly higher rate of comorbidities including psychiatric illness burden compared with the non-narcolepsy population.
BALTIMORE -- Individuals diagnosed with narcolepsy appear to have more comorbidities -- psychiatric and nonpsychiatric -- than controls, an analysis of a large database showed.
Compared with controls, patients identified as having narcolepsy, with or without cataplexy, were 3.7 times more likely to have nervous system complications, 3.8 times more likely to have a mental illness, and 2.7 times more likely to have a digestive illness, Jed Black, MD, of the Stanford Sleep Center in Redwood City, Calif., and colleagues reported here at the Associated Professional Sleep Societies meeting.
They were also 3.5 times more likely to have a musculoskeletal problem and 2.2 times more likely to have a genitourinary illness. All the comparisons were significant at P<0.0001.
"The patients with narcolepsy had a substantially higher incidence of these comorbid diseases," Black told MedPage Today at his poster presentation.
"The question people ask us is why this should be, and we have the same question," he said. "We don't know. We have hypothesized: Does it have something to do with sleep fragmentation? Narcolepsy is not like insomnia. They have profound sleep fragmentation. They have multiple awakenings during the night.
"So we wonder if sleep fragmentation has an impact on other areas of health. There is some evidence that may be the case, but we really don't know," Black said.
The epidemiological study, using the Truven Health Analytics Marketscan Research Database, has findings that are in line with several other smaller studies.
"Frankly, we are scratching our heads. It is a big question mark," Black said. "We need to find out."
He said that clinicians should be more vigilant about checking their narcolepsy patients for other diseases and illnesses. "What we are doing is further exploring narcolepsy in hopes of understanding it better and then maybe we can begin to identify why."
The researchers first interrogated the database, which includes health records of 50 million people, and looked for individuals with at least 5 years of medical insurance coverage. "Of that group we identified 9,312 people who were diagnosed with narcolepsy," Black said. "We looked at narcolepsy with cataplexy and narcolepsy without cataplexy and the differences were almost identical. We matched the subjects for age, sex, and race, on a 5-to-1 basis so our comparison groups were 9,312 individuals with narcolepsy and 46,559 individuals without a narcolepsy diagnosis."
In a companion study, Chad Ruoff, MD, also of the Stanford Sleep Center, specifically looked at comorbid psychiatric diseases which were far more frequent among patients with narcolepsy. "The question is whether narcolepsy causes psychiatric disorders or a psychiatric disorder existed before the narcolepsy, and this data set doesn't give us that answer," he said.
Ruoff said previous studies have noted that a lot of psychiatric disorders are diagnosed before narcolepsy, but that may have been because the narcolepsy diagnosis was missed. "Or could they have had a depressive diagnosis and received medications that led to development of narcolepsy? It's a chicken or the egg type of thing," he told MedPage Today.
"We can speculate about why there are more comorbidities with patients who have narcolepsy," Charles Cantor, MD, of the Penn Sleep Clinic and the Perelman School of Medicine at the University of Pennsylvania, told MedPage Today. "But we really don't know the answer."
He said that people with narcolepsy have low self-esteem, have limited employment opportunities, and have limited social engagements which would dispose them towards having depression and other psychiatric morbidities.
Physical injuries such as falls could be associated with cataplexy or narcolepsy; injuries could be due to sleepiness; metabolic syndrome conditions might be due to less activity, he suggested. "Genitourinary illness? I don't know why that would occur more often," he said. "Digestive disease? I don't know why. Infectious disease? I don't know."