Breathing pattern awake and asleep in myotonic dystrophy.

Because myotonic dystrophy patients show marked irregularities of breathing both awake and asleep, variables related to breathing pattern under both conditions were measured in 11 patients, together with pulmonary function indices, ventilatory CO2 response and maximal mouth pressures. The aim of the study was to detect and explain a possible interrelationship between daytime and nocturnal irregularity. Awake, patients demonstrated significantly more variability in tidal volume and respiratory cycle time than controls. Asleep, periodic breathing occurred during up to 100% of the time spent in light sleep, but not during deep sleep. A strong correlation was found with age (r = 0.73, p = 0.01). No relationship was found between disturbed breathing awake and asleep. There was a tendency for increased variability of tidal volume awake in cases with a decreased ventilatory CO2 response (p = 0.1). The results indicate that different mechanisms may be involved in daytime and nocturnal irregularity. It is hypothesized that brain stem integrative functions may be impaired in myotonic dystrophy.

Daytime sleep in myotonic dystrophy is not caused by sleep apnoea.

Daytime sleepiness is common in myotonic dystrophy and might be attributed to disturbed nocturnal breathing. Seventeen out of 22 patients complained of excessive daytime sleepiness, resembling "idiopathic hypersomnolence". Sleep apnoea might have contributed to daytime sleepiness in only three of 17 patients. Treatment with the central stimulant methylphenidate produced sustained benefit in seven out of 11 patients tested. Daytime sleepiness in myotonic dystrophy is usually caused by dysfunction of central sleep regulation and not by disturbed nocturnal breathing.