Cause:Genetic, sex-linked; occasionally autosomal recessive
Pathophys:Decreased calcium uptake, but normal muscle efficiency early in course of disease affecting both fast and slow fiber bundles (Nejm 1969;280:184); deficient dystrophin, a muscle protein (Nejm 1988;318:1363)
Sx:
Aggressive: onset age 1-5 yr. Calf hypertrophy early, later may decrease; symmetric pelvic involvement, w waddle gait and Gowers' si
Benign: onset usually age 6-18 yr, but can range 2-35 yr. Calf, deltoid, infraspinatus hypertrophy; pelvic 1st, then shoulder in pts age 5-10 yr
Si:As above
Aggressive: relentless, often rapid progression, in bed by age 10 yr
Benign: able to walk 25-30 yr after onset; life expectancy into 4th-5th decades
Progressive skeletal deformities; death due to wasting, inanition, infection; pseudo-gi obstruction and gastric dilatation due to smooth muscle involvement (Nejm 1988;319:15); myocardiopathy in both patients and female carriers (83%), gradually progressive (Jama 1996;275:1335)
r/o metabolic myopathies: acid maltase deficiency; carnitine deficiency (Nejm 1985;312:370); other sex-linked muscular dystrophies: Becker's dystrophy, and Emery-Dreifuss muscular dystrophy (Ann IM 1993;119:900)
Lab:
Chem:Elevated CPK (in carrier females too), aldolase, and AST (SGOT); all elevated early before clinical sx and si, decrease later with burnout
Path:Muscle bx shows dystrophy before clinical sx and si's, ie, random-sized fibers; lipomatosis; increased connective tissue in interstitium; degenerative changes like hyalinization, vacuolization, etc; nuclear shrinkage; basophilic staining of some fibers
Rx:
Prevent by prenatal dx at age 18-20 wk in utero via amniotic CPK (Nejm 1977;297:968); or DNA probe techniques via amniocentesis sample of early pregnancy (Nejm 1987;316:985) or by activation of myogenesis (Nejm 1993;329:915)
Prednisone 0.75 mg/kg qd × 6 mo increases strength (Nejm 1989;320:1592)