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 Arthritis: Various viral infections can cause joint pain, such as parvovirus B19, which is common in adolescents.
Hypermobility Syndrome: Also known as Ehlers-Danlos syndrome, it can cause joint pain due to excessive joint mobility.

Lupus: Systemic lupus erythematosus (SLE) is an autoimmune disease that can present with joint pain, among other systemic symptoms. It's crucial to diagnose early due to its potential for serious complications.
Rheumatic Fever: Although less common, it can occur after a streptococcal infection and presents with joint pain, among other symptoms.
Osteomyelitis or Septic Arthritis: Infections within the bone or joint can cause severe pain and have serious consequences if not treated promptly.
Cancer (e.g., Leukemia, Lymphoma): Certain types of cancer can initially present with joint pain due to bone marrow involvement or metastasis.

Sarcoidosis: A condition that can cause joint pain due to granulomatous inflammation, though it's less common in adolescents.
Mixed Connective Tissue Disease: An autoimmune disorder that overlaps with lupus, scleroderma, and rheumatoid arthritis, presenting with joint pain among other symptoms.
Relapsing Polychondritis: A rare condition characterized by recurrent episodes of cartilage inflammation, which can cause joint pain.