A 6-year-old boy experiences leg pain only at night with no systemic symptoms. What is the diagnosis?

The diagnosis of growing pains is appropriate in this scenario involving a 6-year-old boy who experiences leg pain only at night without any systemic symptoms. Growing pains are common in children and are often described as bilateral pain affecting the legs, typically occurring in the late afternoon or evening, and they can wake the child from sleep. These pains are usually self-limiting and resolve with time.

The absence of systemic symptoms such as fever, swelling, or significant tenderness at specific sites helps differentiate growing pains from other conditions that might present similarly. For example, conditions like acute hematogenous osteomyelitis would likely feature systemic symptoms, including fever and possibly localized swelling or tenderness over the affected bone.

In contrast, Osgood-Schlatter disease usually presents with knee pain related to physical activity, particularly in more active children, and is associated with tenderness over the tibial tuberosity. Sever's disease typically causes heel pain in active children and is related to inflammation of the growth plate in the heel.

Given that the boy's pain is specific to nighttime and he does not have any associated signs of systemic illness or particular localized findings, growing pains represent the most fitting diagnosis.