Muscular Dystrophies group of inherited myopathic disorders characterized by progressive muscle weakness and wasting. A number of skeletal muscle genes have now been associated with the different muscular dystrophies. Defects of these genes lead to abnormalities of corresponding skeletal muscle proteins may lead to a greater susceptibility to necrosis of muscle fibers, but the molecular mechanisms involved are not yet clear.

They classified into many classes based on genetic grounds. There is no specific treatment for the muscular dystrophies. It is important to encourage patients to lead as normal a life as possible. Deformities and contractures often can be prevented or ameliorated by physical therapy and orthopedic procedures. Prolonged bed rest must be avoided, as inactivity often leads to worsening of disability.

Duchene Dystrophy The most common form of muscular dystrophy, X-linked disorder, predominantly affects males, Symptoms begin by age 5 years, patients are typically severely disabled by adolescence death occurring typically in the third decade, Toe walking, waddling gait, and an inability to run are early symptoms. Weakness is most pronounced in the proximal lower extremities but also affects the proximal upper extremities. Gower's sign +ve, Pseudohypertrophy of the calves.

Gowers’ sign showing a patient using arms to climb up the legs in attempting to get up from the floor.

the heart is involved late in the course, and mental retardation is a frequent accompaniment, serum CPK levels are exceptionally high. The gene in question is located on the short arm of the X chromosome and codes for the protein dystrophin, which is absent or profoundly reduced in muscles from patients with the disorder, The absence of dystrophin from synaptic regions of cerebral cortical neurons may contribute to mental retardation

No definitive treatment is available, but prednisone, 0.75 mg/kg/d orally, may improve muscle strength for up to 3 years. Deflazacort (0.9 mg/kg/d), an analogue of prednisone, is probably as effective as prednisone but with fewer side effects, Creatine monohydrate (5–10 g/d) may also be beneficial.

Becker Dystrophy X-linked Less common than Duchene dystrophy weakness similar to that observed in Duchene dystrophy Pseudohypertrophy occurs but to less degree than that in Duchene dystrophy Its average onset (11 years) and However age at death is late (42 years) Cardiac and cognitive impairment do not occur, serum CK levels are less strikingly elevated than in Duchene dystrophy. In contrast to Duchene dystrophy, dystrophin levels in muscle are normal in Becker dystrophy, but the protein is qualitatively altered. It is not clear whether steroids have any role in treatment of this dystrophinopathy.

Limb-Girdle (Erb) Dystrophy in classic form inherited in autosomal dominant but could be autosomal recessive or sporadic begins clinically between late childhood and early adulthood. In contrast to Duchene and Becker dystrophies, the shoulder and pelvic girdle muscles are affected to a more nearly equal extent, & pseudohypertrophy is not seen, and serum CK levels are less elevated. It has variable severity & rate of progression; & there may be sever disability in middle life. No mental impairment Cardiac involvement is rare

Facioscapulohumeral Dystrophy autosomal dominant usually start in adolescence compatible with a normal life span, clinical severity of this condition is highly variable, weakness is typically confined to the face, neck, and shoulder girdle, but foot drop can occur, winged scapulae are common, the heart is not involved, serum CK levels are normal or only slightly elevated.

Facioscapulohumeral dystrophy with prominent scapular winging.

Oculopharyngeal Dystrophy autosomal dominant, more common in Quebec and the southwestern United States often begins in the third to fifth decade, findings include: ptosis, total external ophthalmoplegia, dysphagia, facial weakness, and often proximal limb weakness, serum CK is mildly elevated, dysphagia is particularly incapacitating and may require nasogastric feeding or gastrostomy

Myotonic Dystrophies Myotonic dystrophy type 1 (DM1): ― is a dominantly inherited disorder ― usually is manifest in the third or fourth decade, although it may appear in early childhood ― there are myotonia (delay in relaxations) accompanies weakness and wasting of the facial, sternomastoid, and distal limb muscles ― There may also be cataracts, frontal baldness, testicular atrophy, diabetes mellitus, cardiac abnormalities, and intellectual changes

Congenital myotonic dystrophy is a more severe form of DM1 and occurs in 25% of infants of affected mothers. ― It is characterized by severe facial and bulbar weakness, transient neonatal respiratory insufficiency, and mental retardation. ― Muscle stiffness (in contrary to the real myotonia) is enhanced by cold and inactivity and relieved by exercise.

Myotonia is demonstrable by percussion of the thenar eminence, the tongue, and wrist extensor muscles. Myotonia causes a slow relaxation of hand grip after a forced voluntary closure. Advanced muscle wasting makes myotonia more difficult to detect.

myotonic dystrophy type 2 (DM2): ― has a distinct pattern of muscle weakness affecting mainly proximal muscles & hence the term proximal myotonic myopathy . ― Other features of the disease overlap with DM1, including cataracts, testicular atrophy, insulin resistance, constipation, hypersomnia, and cognitive defects. ― Cardiac conduction defects occur but are less common, and the hatchet face and frontal baldness are less consistent features ― A very striking difference from DM1 is the failure to clearly identify a congenital form of DM2.

Investigations: Serum CK levels may be normal or mildly elevated. EMG evidence of myotonia is present in most cases: “characteristic high-frequency discharges of potentials that wax and wane in amplitude and frequency, producing over the EMG loudspeaker a sound like that of a dive bomber or chain-saw”. Muscle biopsy shows selective type 1 muscle fibers atrophy in 50% of cases. Typically, increased numbers of central nuclei can be seen. Necrosis of muscle fibers and increased connective tissue, common in other muscular dystrophies, do not usually occur in myotonic dystrophy.

Treatment: Myotonia can be treated with quinine sulfate, 300 –400 mg three times daily; procainamide, 0.5 – 1 g four times daily; or phenytoin, 100 mg three times daily. In myotonic dystrophy, phenytoin is perhaps the drug of choice, since the other drugs may have undesirable effects on cardiac conduction. There is no treatment for the weakness that occurs, pharmacologic maneuvers do not influence the natural history (treatment is merely symptomatic).

Cardiac pacemaker insertion should be considered for patients with unexplained syncope or advanced conduction system abnormalities with evidence of second-degree heart block, or trifascicular conduction disturbances with marked prolongation of the PR interval. Molded ankle-foot orthoses help prevent foot-drop in patients with distal lower extremity weakness.