What are the differential diagnoses for a left wrist bony prominence near the thumb?

Differential Diagnoses for Left Wrist Bony Prominence Near the Thumb

The most likely diagnosis for a bony prominence at the left wrist near the thumb is thumb base (carpometacarpal joint) osteoarthritis, which characteristically presents with bony enlargement at this location. 1

Primary Differential Diagnoses

Thumb Base Osteoarthritis (First CMC Joint OA)

• Bony enlargement with or without deformity (including subluxation and adduction of the thumb base) is a clinical hallmark of hand osteoarthritis affecting this characteristic target site. 1
• Typically presents with pain on usage and mild morning stiffness, with symptoms often intermittent. 1
• Risk factors include female sex, age over 40, menopausal status, family history, and prior hand injury. 1
• Plain radiographs showing joint space narrowing, osteophytes, subchondral sclerosis, and subchondral cysts confirm the diagnosis. 1

Ganglion Cyst

• The most common wrist mass overall, though typically presents as a soft rather than bony prominence. 2
• Can occur at the radial aspect of the wrist near the thumb base. 2
• Distinguished from bony prominences by its cystic nature on palpation and imaging. 2

de Quervain Tenosynovitis

• Involves the first dorsal compartment (abductor pollicis longus and extensor pollicis brevis tendons) at the radial styloid. 3
• A positive Finkelstein test is pathognomonic, but care must be taken to differentiate this from thumb carpometacarpal arthritis. 3
• Presents with pain and swelling rather than true bony prominence, though chronic inflammation can cause apparent thickening. 3

Gout

• Gout can superimpose on pre-existing hand osteoarthritis, complicating the clinical picture. 4
• While gout more commonly affects metacarpophalangeal joints and wrists, it can involve the thumb base area. 4
• Presents with acute inflammatory episodes rather than chronic bony prominence. 4

Rheumatoid Arthritis

• Rheumatoid arthritis mainly targets metacarpophalangeal joints, proximal interphalangeal joints, and wrists, but can involve the thumb. 1
• Deformities arise from inflammatory soft tissue changes, ligament stretching, and tendon subluxations. 5
• Distinguished by soft tissue swelling, synovitis, and symmetric involvement rather than isolated bony prominence. 1

Psoriatic Arthritis

• May affect just one ray or target distal interphalangeal joints. 1
• Can involve the thumb in isolation. 4
• Associated with skin or nail psoriasis and inflammatory features. 1

Haemochromatosis Arthropathy

• Mainly targets metacarpophalangeal joints and wrists. 1, 4
• Less commonly involves the thumb base specifically. 1
• Associated with systemic iron overload findings. 1

Diagnostic Approach

Initial Evaluation

• Radiography is always indicated as initial imaging for suspected wrist pathology, with a 3-view examination (posteroanterior, lateral, and oblique) being standard. 1
• Look for joint space narrowing, osteophytes, subchondral sclerosis, and cysts characteristic of osteoarthritis. 1
• Assess for erosive changes that might suggest inflammatory arthritis. 1

When Initial Radiographs Are Equivocal

• CT without IV contrast is commonly used to exclude or confirm suspected wrist pathology when radiographs are equivocal. 1
• MRI without IV contrast can detect occult fractures and soft tissue pathology. 1
• Blood tests are not required for diagnosis of hand osteoarthritis but may be needed to exclude coexistent inflammatory disease if marked inflammatory symptoms are present. 1, 6

Key Clinical Distinctions

The location near the thumb base strongly suggests thumb carpometacarpal osteoarthritis as the primary diagnosis, as this is a characteristic target site for osteoarthritis. 1 The presence of true bony prominence (rather than soft tissue swelling) further supports degenerative rather than inflammatory pathology. 1

Common Pitfalls to Avoid

• Confusing de Quervain tenosynovitis with thumb carpometacarpal arthritis—both present with radial-sided wrist pain near the thumb. 3
• Overlooking gout superimposed on pre-existing osteoarthritis, which can complicate the clinical picture. 4
• Failing to obtain adequate radiographic views (minimum 3 views) for proper assessment. 1