De Quervain's Tenosynovitis: This condition, which affects the tendons on the thumb side of your wrist, is a common cause of pain at the base of the thumb. It often occurs without any specific trauma, making it a likely candidate for the described symptoms.

Osteoarthritis of the First Carpometacarpal Joint: This is a common condition that affects the joint at the base of the thumb, leading to pain and stiffness. It can develop over time without a specific traumatic event.
Thumb Carpometacarpal Joint Instability: Instability in this joint can cause pain at the base of the thumb, especially during certain movements or activities.
Ganglion Cyst: A ganglion cyst is a lump or mass that can develop near joints or tendons, including at the base of the thumb, and can cause pain.

Giant Cell Tumor of the Tendon Sheath: Although rare, this tumor can cause pain and swelling at the base of the thumb. Early diagnosis is crucial for effective treatment.
Infection (e.g., Septic Arthritis or Osteomyelitis): Infections in the joint or bone at the base of the thumb can cause severe pain and have serious consequences if not promptly treated.
Nerve Compression (e.g., Radial or Median Neuropathy): Compression of nerves in the wrist or hand can cause pain at the base of the thumb, along with other symptoms like numbness or tingling.

Sarcoidosis: This autoimmune disease can cause inflammation and pain in various parts of the body, including the joints and tendons at the base of the thumb.
Tuberculous Tenosynovitis: A rare form of tuberculosis that affects the tendons, which can cause chronic pain and swelling at the base of the thumb.
Erythromelalgia: A disorder that causes burning pain, heat, and redness in the hands and feet, which could potentially affect the base of the thumb.