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muscles are weaker than the distal muscles These children have large, rubbery, hypertrophic calf muscles without tenderness DTRs are present early, but disappear later Sensory examination is normal The diagnosis is supported by a creatine kinase (CK) elevation that may range from 10 to 10,000 times normal, and is confirmed by muscle biopsy Death occurs from progressive respiratory insufficiency or infection, dysrhythmia secondary to cardiomyopathy, or congestive heart failure Becker muscular dystrophy is also an X-linked recessive MD, but is less severe, with a later presentation, intact IQ, preservation of ambulation, rare cardiac involvement, and favorable survivability Myotonic dystrophy is an autosomal-dominant, multisystem disorder that presents from infancy to adolescence with myotonia and distal muscle weakness Its classic feature, myotonia, is defined as a disturbance in muscle relaxation after contraction It causes an inability to quickly relax a contracted muscle or release an object Unlike MG, this myotonia is worsened by rest A characteristic facial weakness, the “Cheshire cat smile,” is an inability for a child to relax a smile Dermatomyositis is a systemic angiopathy that is manifested by intravascular occlusion and infarction in muscles, connective tissue, skin, the gastrointestinal tract, and small nerves (see Chapter 101 Rheumatologic Emergencies ) It is caused by antibody or immune complex–mediated immune response against a vascular endothelial component Patients commonly present with fever, anorexia, and fatigue, followed by rash, and then the myositis The classic heliotrope rash is a violaceous discoloration and edema of periorbital and malar areas Over time, the rash spreads to the extensor surfaces of the joints Papular, erythematous, scaly lesions over the knuckles are referred to as the Gottron sign Arthralgias and cardiac complications are common Polymyositis , a similar disorder, is rare in children Infectious processes of the muscle may also present with weakness Pyomyositis is caused by multifocal abscesses associated with a bacterial infection of the muscle Causative agents include S aureus, streptococci, Escherichia coli , Yersinia , and Legionella species Although most common in immunocompromised patients, it can also occur in normal hosts Clinical presentation includes muscle pain, tenderness, and fever A septic joint can cause a pseudoparalysis of a single limb in young infants Extreme pain should result from moving the affected limb Viral myositis is one of the more common causes of acute weakness seen in children ( Table 82.4 ) and commonly follows influenza or other viral respiratory illness Several days of prodromal constitutional symptoms lead to severe symmetric muscle pain and generalized weakness On examination, the muscles
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