Differentials
Rheumatoid arthritis (RA)
SIGNS / SYMPTOMS
A symmetric polyarthritis commonly affecting the small joints of the hands and feet.
RA does not affect the lumbar spine or sacroiliac joints.
Dactylitis is not a feature.
INVESTIGATIONS
Rheumatoid factor and anti-cyclic citrullinated peptide (anti-CCP) antibodies may be positive.
Hand radiographs reveal typical erosive changes at the margins of the joint, affecting the subchondral bone first and later progressing to cause joint space narrowing.
Gout
SIGNS / SYMPTOMS
History of an acute and relapsing course with resolution of the synovitis within 7-14 days should raise the suspicion of possible gout.
Swelling, effusion, warmth, erythema, and/or exquisite tenderness of the involved joint(s).
Most commonly involved joints are in the feet, especially the first metatarsophalangeal, tarsometatarsal, and ankle joints.
Pattern is usually monoarticular or oligoarticular (<4 joints). Can be polyarticular, affecting multiple joints in the hands and feet, especially in older people.
Tophi may be present over extensor surface joints, especially the elbows, knees, and Achilles tendons. May also be evident over dorsal aspects of hands and feet, and in the helix of the ears.
INVESTIGATIONS
Synovial fluid exam will reveal strongly negative birefringent, needle-shaped crystals under polarized light.
Erosive osteoarthritis
SIGNS / SYMPTOMS
Occurs most commonly in middle-aged women.
Affects the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints of the fingers only.
INVESTIGATIONS
Plain film radiographs will show typical changes of osteoarthritis involving the DIP and PIP joints with associated marginal or central bone erosions resulting in the characteristic gull-wing deformity.
Reactive arthritis
SIGNS / SYMPTOMS
Recent exposure to certain gastrointestinal and genitourinary infections, particularly Chlamydia species, Campylobacter jejuni, and Salmonella enteritidis.
Oligoarthritis, commonly affecting weight-bearing joints. May also have inflammation at the site of tendon insertion and dactylitis (whole-digit inflammation).
Extra-articular manifestations such as conjunctivitis, urethritis, and stomatitis may be present.
INVESTIGATIONS
X-rays may show soft-tissue swelling.
Urine screen for Chlamydia trachomatis may be positive.
Mycobacterial tenosynovitis
SIGNS / SYMPTOMS
Dactylitis-like swelling of a single digit may be observed.
Mycobacterium tuberculosis and atypical mycobacteria have both been implicated.
INVESTIGATIONS
Synovial biopsy and culture will most commonly isolate a rapidly growing mycobacterium from the tissue.
Sarcoid dactylitis
SIGNS / SYMPTOMS
Dactylitis is observed in some patients with chronic sarcoid, especially those with cutaneous and osseous disease.
Signs suggestive of underlying sarcoid usually present (e.g., cough, dyspnea, wheezing, lymphadenopathy, skin lesions).
INVESTIGATIONS
Chest-x-ray: hilar adenopathy and/or features of interstitial lung disease.
Plain film radiographs of the hands and feet may show cystic bone lesions in the phalanges.
Biopsy of suspicious skin lesion will reveal noncaseating granulomas.
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