Rarely it may occur in patients with functional lesions the circadian clock, including those with neurologic ablation due to tumor or other pathological process. Limiting daytime napping, increased outdoor activity, etc. Bright light therapy. Sleep occurs intractably later than the desired time. It is subsequently difficult for the patient to awaken at the desired time.
Daytime somnolence is limited to the morning hours.
Pathogenesis is controversial. Direct evidence of these models are lacking. The behavioral features of DSPS have led to the speculation that the disorder occur as a consequence of behavior rather than a consequence of an inherent or underlying abnormality of circadian clock function. By successively delaying the sleep of these patients, it was possible to achieve the desired phase position without requiring the intrinsic clock to advance. Chronotherapy is likely to be difficult without careful control of light exposure.