Ans.D. Acute viral myositisThe clinical picture suggests the most probable diagnosis is Viral myositis. The specific history of URI suggests influenza myositis. Infectious myositis has a male predominance and are typically seen in young adults. The typical presentation of the childhood form includes fever, malaise, and rhinorrhea which is usually followed in 1-7 days by severe pain, especially in the calves. The muscle pain is usually worse with movement and the symptoms last for about a week. Muscle weakness, tenderness, and swelling are usually seen with more severity in adults and the Proximal muscles are affected predominantly.In children, toe walking and wide-based gait may be seen because of the involvement of the gastrocnemius-soleus muscles. Lab features of influenza myositis includeElevated CK may be as high as 500 times normalUrine myoglobin is usually positive