Differentials
Psoriatic arthritis (PsA)
SIGNS / SYMPTOMS
Commonly involves small joints of the hands and feet but is less often symmetrical. Fewer than 5 joints are commonly affected (oligoarthritis). Distal interphalangeal (DIP) joint involvement is more common in psoriatic arthritis than rheumatoid arthritis (RA).
Psoriasis is present in >90% of PsA patients, but is unusual in RA patients.
INVESTIGATIONS
PsA is for the most part seronegative, even though there are patients with low levels of rheumatoid factor (RF) diagnosed with PsA because of presence of psoriasis.
Skin biopsy of suspicious lesions can show psoriasis, supporting the diagnosis.
Infectious arthritis
SIGNS / SYMPTOMS
Direct infection of a joint is rare, and urgent specialist advice should be obtained if suspected. Reactive arthritis, where there is no direct infection in the joint, can cause symmetric hand and feet arthritis and can be seen after viral/bacterial infections.
INVESTIGATIONS
Most resolve within 6 weeks and leave no long-term effects.
Gout
SIGNS / SYMPTOMS
A small percentage of gout patients present with polyarticular gout, which can mimic rheumatoid arthritis (RA). Tophi and high levels of uric acid are specific for gout, but are very rare in RA. In addition, erosions seen in gout where the tophi have eroded into the bone differ from the erosions seen in RA.
INVESTIGATIONS
Serum uric acid >416 micromols/L (>7 mg/dL), urate crystals from the joint aspirate or tophus. Tophus eroding into the joint in gout is more destructive and much larger; RA erosions are more limited to cartilage-bone interface and tend to be smaller.
Systemic lupus erythematosus
SIGNS / SYMPTOMS
Systemic lupus erythematosus (SLE) can present with polyarthritis in the small joints of the hands and feet.
SLE arthritis is usually non-deforming.
INVESTIGATIONS
A wide range of autoantibodies seen in SLE help differentiate the two conditions. High antinuclear antibody (ANA) titre, anti-extractable nuclear antigen (ENA) autoantibodies are seen rarely in rheumatoid arthritis.
On radiographs, erosions are not typically seen in the joints of SLE patients.
Osteoarthritis
SIGNS / SYMPTOMS
Prevalence increases with age. The most commonly affected joints are the knee, hip, hands, and lumbar and cervical spine. Patients present with joint pain and stiffness that is typically worse with activity.
INVESTIGATIONS
Radiographs show loss of joint space, subchondral sclerosis, and osteophytes.
Adult-onset Still’s Disease
SIGNS / SYMPTOMS
Intermittent high-spiking fever, occurring at least daily over a period of at least one week.[73]
Arthralgia/arthritis, most commonly affecting the proximal interphalangeal joints, wrists, elbows, knees, and ankles.[74][75][76][77][78][79]
Salmon-pink, maculopapular skin rash, occurring transiently during fevers.
Other common symptoms include pharyngitis, myalgia, and pleuritis.
INVESTIGATIONS
Largely a diagnosis of exclusion after ruling out infections, malignancy, and other rheumatological conditions.
Hyperferritinaemia is a sensitive but poorly specific marker. The combination of markedly elevated serum ferritin (≥5 x ULN) together with glycosylated ferritin <20% (if test is available) can act as a sensitive and specific marker.[80][81][82]
Calcium pyrophosphate deposition
SIGNS / SYMPTOMS
Acute CPPD causes erythema, warmth, and swelling of the affected joint.
Fever and constitutional symptoms may also be present.
The knee is the most commonly affected joint, followed by the wrist.
Use of this content is subject to our disclaimer