A 7 year old boy with progressive muscle weakness and walking difficulties presented with the following finding. What is the probable diagnosis?

A boy with progressive muscle weakness, walking difficulties, and the image showing pesudohyperophy of calf muscles is suggestive of Duchenne muscular dystrophy (DMD). Pseudohyperophy of calf muscles is the characteristic feature of DMD, where as other 3 conditions mentioned in option donot have this feature. Duchenne Muscular Dystrophy: Most common hereditary neuromuscular disease It is an X-linked recessive disorder, and the causative gene is located at Xp21 Clinical features: Progressive weakness with developmental delay occurs Pesudohyperophy of calves and wasting of thigh muscles is seen. Tredelenburg gait or hip waddle is characteristic Gower&;s Sign: Indicates weakness of proximal muscles: The patient has to use hands and arms to "walk up" their own body from a squatting position Dilated cardiomyopathy Diagnosis: Elevated serum creatine kinase levels Polymerase chain reaction(PCR) analysis for dystrophin gene If PCR is normal, but clinical suspician is high, muscle biopsy with dystrophin immunocytochemistry is done. Treatment: Treatment of cardiac decompensation, nutritional management, Physiotherapy and glucocoicoids. Prognosis: Death occurs usually at about 18 to 20 years of age due to respiratory failure, intractable hea failure, pneumonia, or aspiration Ref: Nelson textbook of pediatrics 21st edition Pgno: 3281