Osteoarthritis (OA): The most common cause of DIP joint involvement, characterized by degenerative changes, joint space narrowing, and the formation of Heberden's nodes. OA is a wear-and-tear arthritis that commonly affects the DIP joints.

Psoriatic Arthritis (PsA): A form of arthritis that occurs in some people with psoriasis, often involving the DIP joints, and can lead to significant joint damage if not treated. The presence of psoriatic skin lesions and nail changes can aid in diagnosis.
Rheumatoid Arthritis (RA): Although RA more commonly affects the MCP and PIP joints, it can also involve the DIP joints, especially in late or severe disease. Symmetrical joint involvement and systemic symptoms are key features.
Gout: Gouty arthritis can affect any joint, including the DIP joints, and is characterized by sudden, severe attacks of pain, swelling, redness, and tenderness. Urate crystals in the joint fluid confirm the diagnosis.

Septic Arthritis: An infection within a joint, which is a medical emergency requiring prompt diagnosis and treatment to prevent joint destruction. Fever, significant pain, and swelling are typical presentations.
Lyme Arthritis: Caused by the bacterium Borrelia burgdorferi, transmitted by ticks. It can cause arthritis that may involve the DIP joints among others, and is diagnosed through a combination of clinical presentation, serologic testing, and sometimes joint fluid analysis.

Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. Some types can lead to early-onset osteoarthritis, including DIP joint involvement.
Hemochromatosis: A genetic disorder characterized by excessive iron accumulation in the body, leading to various organ damages, including arthropathy that can involve the DIP joints.
Sarcoid Arthritis: A condition where sarcoidosis, an inflammatory disease, affects the joints. It can cause arthritis in various joints, including the DIP joints, though this is less common.