De Quervain's Tenosynovitis: This condition, which affects the tendons on the thumb side of the wrist, is a common cause of wrist and thumb pain, especially with activities that involve gripping or twisting.

Carpal Tunnel Syndrome: Although it primarily affects the median nerve, causing symptoms in the thumb, index, middle finger, and part of the ring finger, it can also cause wrist pain and is a common condition.
Osteoarthritis of the Thumb: Arthritis in the joint at the base of the thumb can cause pain and stiffness, particularly with gripping or twisting motions.
Ganglion Cyst: A common benign lump that can occur on the wrist, which may cause pain, especially if it presses on a nerve.

Fracture (Scaphoid or Other Carpal Bones): A fracture in the wrist, particularly of the scaphoid bone, can cause pain in the wrist and thumb area. Missing this diagnosis can lead to complications like non-union or avascular necrosis.
Infectious Tenosynovitis: An infection within the tendon sheaths can cause severe pain, swelling, and redness, and if not treated promptly, can lead to serious complications.
Gout or Pseudogout: These conditions can cause sudden, severe pain and swelling, often affecting the wrist or base of the thumb, and require specific treatment to manage symptoms and prevent long-term damage.

Giant Cell Tumor of the Tendon Sheath: A rare, benign tumor that can occur in the wrist or thumb, causing pain and swelling.
Kienbock's Disease: A rare condition where the blood supply to one of the bones in the wrist (the lunate) is interrupted, leading to its collapse and causing wrist pain.
Sarcoidosis: A systemic disease that can cause inflammation and pain in various parts of the body, including the wrists and hands, though this would be a rare presentation.