−Death usually around age 18 years from respiratory failure in sleep, intractable heart failure, pneumonia, aspiration with obstruction
•Lab studies
−CPK—15,000–35,000 U/L (normal is <160 U/L) (initial screen for myopathy)
−Best initial test—molecular genetic diagnosis: deficiency or defective dystrophin cytoskeletal protein from gene at Xp21.2
−Muscle biopsy to show the abnormal or absent dystrophin; most accurate test (do if dystrophin-negative)
•Treatment—multidisciplinary team
−Digoxin for heart failure (all patients need cardiology referral)
−Vigorous treatment of pulmonary infections
−Maintain good nutrition; good calcium supply (prevent osteoporosis)
−Physiotherapy—delay contractions; orthotic devices, proper wheelchair, physiatrist
Myotonic Dystrophy
Myotonic dystrophy is the second most common muscular dystrophy.
•Autosomal dominant inheritance; CTG trinucleotide expansion at 19q13.3; causes multiple dysfunctions in multiple organ systems
•Involves both striated and smooth muscle
•Most common findings may be present at birth; the severe congenital form occurs in a baby born to a mother with symptomatic disease:
−Facial wasting: Inverted V-shaped upper lip, thin cheeks, scalloped concave temporalis muscles, narrow head, high arched palate
−Hypotonia: mild weakness and progressive wasting of DISTAL muscles especially hands, then dorsal forearm and anterior compartment of lower leg, then atrophy of proximal muscles
−Progressive difficulty in climbing steps and lastly a Gower sign
−Slow progression through childhood to adulthood but rare to lose ability to walk
−NOTE: The distal distribution of muscle wasting is the exception to the general rule of myopathies having a proximal and neuropathies a distal distribution
−Myotonia: not evident until age >5; very slow relaxation of muscle after a contraction, but NOT a painful muscle spasm (difficulty opening fist or relaxing grip)
•Other problems:
−Poor speech articulation, slurred
−Difficulty swallowing, aspiration pneumonia
−Extraocular muscle weakness; cataracts
−Slow GI emptying, constipation
−Ineffective uterine contractions
−Heart block and arrhythmia (not cardiomyopathy as in other dystrophies)
−Many endocrine problems
° Half with intellectual impairment
•Diagnosis: CPK as a screen (in the hundreds compared to MD); EMG classic myotonic findings; best test is DNA (blood); biopsy not needed
•Treatment: supportive
