What percentage of patients with insomnia does not have another identifiable core cause or comorbidity with the insomnia?
Dr. Roth: The most conservative estimate is about 10%, and the most liberal estimate is 25%. A minority of patients have what is euphemistically called “primary insomnia,” or insomnia with no other condition. My guess is that the number is closer to 10% to 15%. However, comorbid insomnia is very different from secondary insomnia, in which a condition or disorder is the primary cause of insomnia. And treating that primary insomnia reverses the insomnia. Most of the insomnia is comorbid with, not secondary to, other conditions. Clinicians may be trained to infer that a patient’s depression causes their insomnia. However, if insomnia is caused by depression, treating depression should, and does, alleviate sleep disruptions. This is not the case if these conditions are comorbid. Dr. Krystal presented data from Breslau and colleagues,2 which shows that in the majority of cases, insomnia precedes the depression. The data show that treating insomnia can actually improve depression. There are
