What is the diagnosis for morning stiffness and gradual loss of motion in a patient under 16 years old?

The diagnosis of morning stiffness and gradual loss of motion in a patient under 16 years old is consistent with juvenile idiopathic arthritis (JIA). JIA is the most common type of arthritis in children and is characterized by inflammation of the joints that lasts for at least six weeks, typically affecting various joints. The clinical presentation often includes symptoms such as morning stiffness, which can limit mobility and functionality, as well as pain and swelling in the affected areas.

In JIA, the gradual loss of motion can lead to significant functional impairment if not managed properly. The condition can also show fluctuations in activity and is associated with other systemic features. The age of onset, persistence of symptoms, and specific joint involvement all contribute to the diagnosis.

Other options presented do not align as closely with the described symptoms. Osteogenesis imperfecta primarily causes bone fragility and fragility fractures rather than joint stiffness and loss of motion. Rheumatic fever, while it can affect joints, usually follows a streptococcal throat infection and presents acutely rather than with chronic stiffness. Systemic lupus erythematosus can affect children but typically includes a variety of systemic symptoms and more acute joint involvement rather than the classic presentation of morning stiffness and gradual motion loss seen in JIA