Differentials
Acute gouty arthritis
SIGNS / SYMPTOMS
Presentation may be identical to that of acute CPP arthritis.
More likely to affect small joints of the lower extremity, particularly the first metatarsophalangeal joint.
Onset is sudden and attack duration is frequently shorter than in acute CPP arthritis.[51]
Risk factors for hyperuricaemia, such as renal insufficiency, are more common.
INVESTIGATIONS
Synovial fluid microscopy is negative for CPP crystals and positive for urate crystals.
Acute septic arthritis
SIGNS / SYMPTOMS
Presentation may be identical to that of gout.
Patients are typically immunocompromised.
INVESTIGATIONS
Synovial fluid microscopy is negative for CPP crystals.
Positive Gram stains or fungal stains, and cultures of synovial fluid.
Milwaukee shoulder syndrome
SIGNS / SYMPTOMS
Typically limited to the shoulders and knees. Effusions are large and, in the shoulders, fluid is often palpable.[52]
INVESTIGATIONS
Synovial fluid microscopy is negative for CPP crystals.
Alizarin red S staining of synovial fluid is positive for CPP crystals.
X-rays show a severe destructive arthropathy, with loss of the rotator cuff, bony destruction, and multiple loose bodies.
Osteoarthritis
SIGNS / SYMPTOMS
Typically affects large weight-bearing joints, the cervical and lumbar spine, and the base of the first metatarsophalangeal joint. In the hands, it involves the first carpometacarpal, distal interphalangeal, and proximal interphalangeal joints.
INVESTIGATIONS
Synovial fluid microscopy is negative for CPP crystals.
X-rays show no evidence of cartilage calcification.
Rheumatoid arthritis
SIGNS / SYMPTOMS
Joints flare simultaneously. Affected joints tend to be in a symmetrical pattern.
INVESTIGATIONS
Synovial fluid microscopy is negative for CPP crystals.
X-rays show typical changes of erosive rheumatoid arthritis.
Polymyalgia rheumatica
SIGNS / SYMPTOMS
Patients complain of prolonged morning stiffness involving the hips and shoulders.
This is typically symmetrical and accompanied by signs and symptoms of systemic inflammation, such as weight loss and malaise.
There is usually little or no synovitis.
INVESTIGATIONS
Synovial fluid microscopy is negative for CPP crystals.
Erythrocyte sedimentation rate is high.
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