Sleep-Wake Cycle and Daytime Sleepiness in the Myotonic Dystrophies

Abstract

Myotonic dystrophy is the most common type of muscular dystrophy in adults and is characterized by progressive myopathy, myotonia, and multiorgan involvement. Two genetically distinct entities have been identified, myotonic dystrophy type 1 (DM1 or Steinert's Disease) and myotonic dystrophy type 2 (DM2). Myotonic dystrophies are strongly associated with sleep dysfunction. Sleep disturbances in DM1 are common and include sleep-disordered breathing (SDB), periodic limb movements (PLMS), central hypersomnia, and REM sleep dysregulation (high REM density and narcoleptic-like phenotype). Interestingly, drowsiness in DM1 seems to be due to a central dysfunction of sleep-wake regulation more than SDB. To date, little is known regarding the occurrence of sleep disorders in DM2. SDB (obstructive and central apnoea), REM sleep without atonia, and restless legs syndrome have been described. Further polysomnographic, controlled studies are strongly needed, particularly in DM2, in order to clarify the role of sleep disorders in the myotonic dystrophies.

Figure 1

Sleep features of a DM1 patient with narcoleptic-like phenotype. (a) Narcoleptic-like hypnogram. Notice the short sleep onset latency, early onset of REM sleep, frequent nocturnal arousals, and REM sleep dysregulation. (b) A 30 s epoch of MSLT of the same patient demonstrating sleep onset REM sleep (SOREMPs). This patient showed 3 SOREMPs in a 4-nap protocol MSLT. ROC & LOC: right and left electrooculogram. F4, F3, C3, C4, T4, T3, O1, and O2: electrode positions according to the 10/20 International System. Chin: electromyography of the mentalis muscle.

Figure 2

Polysomnograms of a DM2 patient showing REM sleep without atonia with dream-enacting behavior history. Eye leads show rapid movements and EEG channels show desynchronized activity; both are features of REM sleep. (a) Excessive phasic electromyographic activity and intermittent increased tonic electromyographic activity in the chin with normal atonia in the limbs during REM sleep. (b) Sustained tonic electromyographic activity in the chin with normal atonia in the limbs during REM sleep. Right eye and left eye: electrooculogram. F4, F3, C3, C4, O1, and O2: electrode positions according to the 10/20 International System, referenced to combined ears (A1, A2). Chin EMG: electromyography of the mentalis muscle. Left and right leg EMG: electromyography of the left and right tibialis anterior. Note the time calibration mark.