Juvenile Idiopathic Arthritis (JIA): This is a common condition in adolescents that presents with joint pain and inflammation. The diagnosis is often made based on clinical presentation and exclusion of other causes.

Fibromyalgia: A condition characterized by widespread musculoskeletal pain, fatigue, and tender points. It's more common in females and can start in adolescence.
Viral or Bacterial Infections: Such as parvovirus, Lyme disease, or rheumatic fever, which can cause joint pain and may be accompanied by other systemic symptoms like fever and rash.
Hypermobility Syndrome: A condition where joints have a greater range of motion than normal, leading to joint pain and instability.

Lupus: Systemic lupus erythematosus is an autoimmune disease that can cause joint pain, skin rashes, and organ damage. Early diagnosis is crucial for effective management.
Rheumatic Fever: A complication of untreated streptococcal infection, which can lead to heart valve damage if not promptly treated.
Osteomyelitis or Septic Arthritis: Infections of the bone or joint, respectively, which are medical emergencies requiring immediate antibiotic treatment.
Cancer (e.g., Leukemia, Lymphoma): Although rare, cancers can present with joint pain and should be considered, especially if accompanied by other symptoms like weight loss, night sweats, or unexplained fatigue.

Ehlers-Danlos Syndrome: A group of genetic disorders affecting connective tissue, leading to hypermobile joints, skin hyperextensibility, and tissue fragility.
Sickle Cell Disease: A genetic disorder that affects hemoglobin production, leading to anemia, episodes of pain (including joint pain), and increased risk of infections.
Mixed Connective Tissue Disease: An autoimmune disorder with features of lupus, scleroderma, and rheumatoid arthritis, which can cause joint pain among other symptoms.