Differential Diagnosis for Pain at the Base of the Right Thumb at the Metacarpophalangeal Joint

• Single Most Likely Diagnosis
  • Osteoarthritis (OA): This is the most common cause of pain at the base of the thumb, particularly at the metacarpophalangeal (MCP) joint. OA leads to cartilage breakdown, causing pain, stiffness, and decreased range of motion. The thumb's MCP joint is a common site for OA due to its high mobility and frequent use.
• Other Likely Diagnoses
  • Rhizarthrosis: Also known as thumb base arthritis, it specifically affects the carpometacarpal joint (CMC) of the thumb but can also involve the MCP joint, causing pain and limited mobility.
  • De Quervain's Tenosynovitis: This condition affects the tendons on the thumb side of your wrist. It can cause pain and tenderness, especially when forming a fist, grasping, or turning the wrist.
  • Trigger Thumb: A condition where the thumb catches or locks when bent, often due to inflammation of the tendon sheath. It can cause pain at the base of the thumb.
• Do Not Miss Diagnoses
  • Gout: Although less common in the thumb, gout can cause sudden, severe pain and swelling in any joint, including the MCP joint of the thumb. Missing this diagnosis could lead to prolonged suffering and potential joint damage.
  • Infection (Septic Arthritis): Bacterial or fungal infections within the joint can cause severe pain, swelling, and redness. Prompt diagnosis and treatment are crucial to prevent joint destruction and systemic infection.
  • Ganglion Cyst: A lump or mass that can develop near joints or tendons, causing pain, especially if it presses on a nerve. Although usually benign, it can cause significant discomfort and needs to be differentiated from other causes.
• Rare Diagnoses
  • Psoriatic Arthritis: A form of arthritis that affects some people with psoriasis, causing joint pain, swelling, and stiffness. It can affect any joint, including those in the thumb.
  • Rheumatoid Arthritis (RA): An autoimmune disorder that can cause pain and swelling in the joints, including the MCP joints of the thumb. It's less common for RA to initially present in the thumb but can be part of a larger pattern of joint involvement.
  • Tumor (Benign or Malignant): Although extremely rare, tumors can occur in the bones or soft tissues around the MCP joint, causing pain and other symptoms.