Dystrophinopathy clinical diagnostic pearls in adults

1. BMD (Becker's) may present in adulthood up to age 50+. Like DMD, earliest muscles involved are glutei, thigh abductors, and triceps, followed by quadriceps, deltoids, tibialis anterior, and last, biceps. Neck FLEXOR weakness is common.

2. The use of prednisone, annual cardiac and pulmonary (including sleep testing) evaluations have made children with DMD survive into the third decade.

3. Muscle cramps with aches during exercise are presentations of BMD during and after teenagehood. Isolated quadriceps involvement in the fifth decade may prompt a confusion with inclusion body myositis.

4. Isolated cardiac failure or even transplantation may occur prior to a diagnosis being made. Decreased LVEF or arrythmias are more common in BMD. X linked dilated cardiomyopathy is a rare form restricted to cardiac muscle with completely normal skeletal muscle, due to mutations that only affect the isoforms of cardiac muscle. Endocardial biopsy is required, and there is 50 % five year mortality without transplantation.

5. Other asymptomatic/minimally symptomatic clinical findings include exertional intolerance, elevated CPK, myalgias, myoglobinuria, none of which are mandatory. Other subtleties include calf and tongue hypertrophy, myopathic EMG, history of clumsiness or toe walking as a child,  and positive family history.

6. Ten percent of female carriers will be symptomatic, many minimally so, and manifest cases will be more likely to have diagnostic mutation on X chromosome. Some may have negative result, and need to be counselled regarding regarding a mutation only expressed in oocytes (germline mutation). For these patients prenatal testing is available (amniocentesis, eg. and others).

7. Coexisting Turners syndrome (XO) or skewed or nonrandom mutation of an X chromosome can cause full blown disease in a female carrier (DMD phenotype).

8. Cognitive disorders are common see http://behavioralneurologynotes.blogspot.com/2010/01/cognition-and-dystrophinopathy.html

9. Annual PSG (polysomnograms) are needed once patients are nonambulatory. Problems with dream sleep are common.

10. GI issues include GI pseudoobstruction in patients on continuous ventilation. This can be relieved by a regular bowel routine, continual low suction, placement of a second jejunal feeding tube. Late, swallowing issues might include positioning for swallowing, and restricted jaw movement due to masseter involvement.