Myotonic Dystrophy

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Myotonic dystrophy (MD) is a common type of muscular dystrophy and is a genetic disorder inherited with an autosomal dominant pattern. Myotonia, muscle weakness, and dystrophic changes in tissue are characteristic features of this disorder. Although this disorder is characterized by the muscle features, it is also associated with cognitive components, facial dysmorphic features, and sleep disturbance. Fatigue, tiredness, and excessive daytime sleepiness are very common in patients with MD.

Sleep apnea in MD patients is common and is more likely to be central than obstructive (84) (Fig. 4). In these patients, nocturnal hypoxemia and hypercapnea are often seen and may be more severe during REM sleep (85) (Fig. 5). Obese MD

Myotonic Dystrophy Occipital Neuralgia

FIGURE 4 Myotonic dystrophy and central apnea. Polysomnography epoch of a patient with myotonic dystrophy demonstrating central sleep apnea. Repetitive electromyographic activity is present in the limb (LAT-RAT) EMG channel. Abbreviations: A2, right auricular (reference) electrode; C3, left central electrode; EKG, electrocardiogram; EMG, submental electromyogram; IC-EMG, intercostal electromyogram; LAT, left anterior tibialis electromyogram; LOC, left outer canthi; LUE, left upper electro-oculogram; Mvt, movement; O1, left occipital electrode; O2 Sat, oxygen saturation; P nasal, nasal pressure; RAT, right anterior tibialis electromyogram; ROC, right outer canthi; RUE, right upper electro-oculogram; Submtl EMG, submental electromyogram; Therm, thermocouple.

FIGURE 4 Myotonic dystrophy and central apnea. Polysomnography epoch of a patient with myotonic dystrophy demonstrating central sleep apnea. Repetitive electromyographic activity is present in the limb (LAT-RAT) EMG channel. Abbreviations: A2, right auricular (reference) electrode; C3, left central electrode; EKG, electrocardiogram; EMG, submental electromyogram; IC-EMG, intercostal electromyogram; LAT, left anterior tibialis electromyogram; LOC, left outer canthi; LUE, left upper electro-oculogram; Mvt, movement; O1, left occipital electrode; O2 Sat, oxygen saturation; P nasal, nasal pressure; RAT, right anterior tibialis electromyogram; ROC, right outer canthi; RUE, right upper electro-oculogram; Submtl EMG, submental electromyogram; Therm, thermocouple.

Submental Emg Electrod

FIGURE 5 Myotonic dystrophy and hypoventilation. Polysomnography epoch of a patient with myotonic dystrophy and hypoventilation. Note the presence of hypercapnea and oxygen desatura-tions in the absence of apneas or hypopneas. Abbreviations: A2, right auricular (reference) electrode; C3, left central electrode; EKG, electrocardiogram; ETCO2, end-tidal CO2; IC-EMG, intercostal electromyogram; LAT, left anterior tibialis electromyogram; LOC, left outer canthi; LUE, left upper electro-oculogram; Mvt, movement; O1, left occipital electrode; O2 Sat, oxygen saturation; P nasal, nasal pressure; RAT, right anterior tibialis electromyogram; ROC, right outer canthi; RUE, right upper electro-oculogram; Submtl EMG, submental electromyogram; Therm, thermocouple.

FIGURE 5 Myotonic dystrophy and hypoventilation. Polysomnography epoch of a patient with myotonic dystrophy and hypoventilation. Note the presence of hypercapnea and oxygen desatura-tions in the absence of apneas or hypopneas. Abbreviations: A2, right auricular (reference) electrode; C3, left central electrode; EKG, electrocardiogram; ETCO2, end-tidal CO2; IC-EMG, intercostal electromyogram; LAT, left anterior tibialis electromyogram; LOC, left outer canthi; LUE, left upper electro-oculogram; Mvt, movement; O1, left occipital electrode; O2 Sat, oxygen saturation; P nasal, nasal pressure; RAT, right anterior tibialis electromyogram; ROC, right outer canthi; RUE, right upper electro-oculogram; Submtl EMG, submental electromyogram; Therm, thermocouple.

patients are at higher risk for nocturnal hypoxemia potentially due to the decreased functional reserve capacity (86). These respiratory disturbances appear to have consequences on general health. Guilleminault (85) discussed that MD patients with sleep apnea, are at risk of developing cardiopulmonary complications such as increased pulmonary and systemic arterial pressure and cardiac arrhythmias during sleep.

SRBD in MD patients may be secondary to a number of factors. Central apneas are probably a manifestation of the effects of the disorder on the CNS and maybe due to loss of catecholaminergic neurons in the medulla or dysfunction of the neurons involved in respiratory control during sleep (87). Reduced functional residual capacity may also result from respiratory muscle dysfunction, volume restriction, and supine position in sleep (84,88).

Technologists should be prepared for the cognitive, cardiac, and respiratory issues involved in patients with MD. Patients may require extra time for explanation and acclimatization to the study environment. Polysomnographic investigation of these patients should include measures of carbon dioxide and nasal pressure for subtle forms of breathing disorders. Technologists should also be attentive to cardiac rhythm and conduction abnormalities. Clinicians and technologists should also expect MD patients to frequently demonstrate sleep-onset REM periods during the overnight and the multiple sleep latency studies.

Treatment of these patients typically involves the use of medication or positive airway pressure support. Some patients respond to medication therapy such as protriptyline or acetazolamide (89). Studies show that patients have a subjective improvement with these medications with little improvement in the apnea index.

Others require pressure support. Due to the high prevalence of central apnea in this population, bilevel positive airway pressure with a timer may be necessary to restore nocturnal ventilation (90). Typically with effective therapy, patients feel better during the day and subjectively report better muscle usage.

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