Misinterpretation of sleep-breathing disorder by periodic limb movement disorder

We report a case of misinterpretation of sleep-disordered breathing due to periodic limb movement disorder. A 67-year-old man was diagnosed with sleep-disordered breathing and subsequently placed on treatment with nasal continuous positive airway pressure (CPAP). The initial diagnostic evaluation did not include measurement of anterior tibialis electromyogram. The respiratory disturbance index of the initial evaluation was 23. After a brief period of nasal CPAP use, the patient discontinued the treatment because no significant change in daytime alertness was noted and signs of CPAP-related insomnia appeared. The patient was restudied polysomnographically with monitoring of anterior tibialis electromyograms. This study identified 392 leg movements of which 65% were associated with brief EEG arousal from sleep. Double-blind analysis of respiratory disturbance and leg movements yielded a total number of 360 arousals in the overnight recording. Eighty-five percent of all respiratory events could be associated with central hypoventilation following periodic limb movement-associated EEG arousal. No significant hypoxia was recorded with these events. We hypothesize that chemoreceptor stimulation secondary to EEG arousal during sleep is responsible for this central hypoventilation. This case report highlights that recording and scoring of leg movements must be an integral part of polysomnographic evaluations.