Trauma or Sprain: This is the most common cause of acute thumb pain, often resulting from a fall onto the thumb or a sudden twisting motion. The mechanism of injury, such as a fall or direct blow, would support this diagnosis.

De Quervain's Tenosynovitis: Inflammation of the tendons on the thumb side of the wrist, which can cause pain and tenderness, especially when forming a fist, grasping, or turning the wrist. Recent repetitive activities or direct pressure on the tendon could justify this diagnosis.
Trigger Thumb: A condition where the thumb catches or locks when bent, often due to inflammation of the tendon sheath. A history of sudden onset or a palpable nodule at the base of the thumb could support this diagnosis.
Osteoarthritis: Wear and tear of the joint cartilage, which can cause pain, stiffness, and limited mobility. A history of gradual onset, especially in older adults, would make this a likely consideration.

Infection (e.g., Paronychia or Felon): Although less common, infections around the nail or in the pulp of the thumb can cause severe pain and have serious consequences if not treated promptly. Signs of infection, such as redness, swelling, warmth, or pus, would necessitate urgent evaluation.
Gout or Pseudogout: Acute inflammatory arthritis that can cause sudden, severe pain in the thumb. A history of similar episodes, especially in other joints, or the presence of risk factors (e.g., kidney stones, certain medications) would raise suspicion for these conditions.
Fracture: A break in one of the bones of the thumb, which could be due to trauma. The mechanism of injury and specific pain location would guide the need for imaging to rule out a fracture.

Ganglion Cyst: A lump under the skin that occurs when the fluid that surrounds joints leaks out and forms a cyst. Although more common on the wrist, it can occur near the thumb, causing pain and discomfort.
Tumor: Benign or malignant growths in the thumb are rare but could cause pain, especially if they impinge on nerves or other structures. Unusual or persistent symptoms not explained by other diagnoses might warrant further investigation for a tumor.
Neuroma: A growth or tumor of nerve tissue, which can cause pain, numbness, or tingling in the thumb. This would be considered if there were symptoms suggestive of nerve involvement and other diagnoses were ruled out.