Respiratory failure occurs in virtually all patients affected with Duchenne dystrophy after they become wheelchair-bound, as well as in some of the other dystrophic diseases. It may be so insidious as to become evident only as sleep apnea, as retention of carbon dioxide that causes morning headache, or as progressive weight loss that reflects the excessive work of breathing. If there are frequent episodes of oxygen desaturation, some improvement in daytime strength and alertness can be attained by assisting ventilation at night. This may be accomplished in the early stages of disease by a negative-pressure cuirass-type of device that expands the chest wall periodically or, more conveniently, by nasal-positive pressure (NIPPV [noninvasive positive-pressure ventilation] or BiPAP [bilevel positive airway pressure]). Later, positive-pressure ventilation through a fenestrated tracheostomy is required that allows nighttime ventilation but leaves the patient free to speak and breathe during the day. With regard to earlier or anticipatory treatment, in patients free of respiratory failure with vital capacities between 20 and 50 percent of predicted values, a randomized trial of nasal mechanical ventilation failed to demonstrate improvement or prolonged survival (Raphael et al). There has been a clinical impression that even more severely affected patients can be managed at home for prolonged periods with respiratory assistance. Needless to say, the common complications of muscular dystrophy—pulmonary infections and cardiac decompensation—must be treated symptomatically. Surgical management of cataracts is indicated when they become mature.
As noted earlier, a vital element in the care of patients with certain of the dystrophies is monitoring for early evidence cardiac arrhythmias. In disorders such as myotonic dystrophy, Emery-Dreifuss dystrophy, the myofibrillar myopathies, and some of the mitochondrial disorders, it is imperative that cardiac status should be evaluated on a regular basis (typically yearly) with ECG and echocardiography and periodically with 24-h rhythm monitoring if the ECG is abnormal or the patient reports episodic symptoms referable to an arrhythmia such as lightheadedness, palpitations, or dyspnea. The timely use of cardiac pacemakers or defibrillators, implemented at the earliest sign of arrhythmia or prophylactically, is often needed in this patient population to reduce the chance of sudden death.
Mexiletine has been shown to reduce myotonia, especially in DM2 and the nondystrophic myotonias as demonstrated in the trial reported by Statland and coworkers but, like quinine that caused rare cardiac arrhythmias, is also now out of favor by some clinicians. Further discussion of myotonia and its treatment can be found in
Chap. 46. Testosterone has been found to increase muscle mass in patients with myotonic dystrophy, but was of no value in preserving strength or lessening myotonia (Griggs et al, 1989).
Vignos, who reviewed the studies that evaluated muscle-strengthening exercises, has offered evidence that maximal resistance exercises, if begun early, can strengthen muscles in Duchenne, limb-girdle, and facioscapulohumeral dystrophies. In the study he conducted, none of the muscles was weaker at the end of a year than at the beginning. Cardiorespiratory function after endurance exercise was not significantly improved. Contractures were reduced by passive stretching of the muscles 20 to 30 times a day and by splinting at night. If contractures have already formed, fasciotomy and tendon lengthening are indicated in patients who are still ambulating, but this is not recommended early in the course of the disease. Maintenance of ambulation and upright posture will delay scoliosis. In general, preventive measures are more successful than restorative ones.