Poly/Monoarthropathies — Approach

An approach to joint pain, from single hot joint to widespread polyarthritis.

Step 1: is this an acute monoarthritis? Exclude septic arthritis first

A single acutely hot, swollen, painful joint is septic arthritis until proven otherwise — a delay in diagnosis and treatment causes significant morbidity and mortality, and joint destruction can occur within days.

• No single test reliably distinguishes infective from inflammatory monoarthritis. Clinical suspicion remains the mainstay of diagnosis; aspirate the joint for cell count, Gram stain and culture before starting antibiotics wherever possible.
• Serum procalcitonin has been studied as an adjunct (a level >0.4–0.5ng/mL favours bacterial infection), but the evidence base is still too limited for it to be recommended as a routine diagnostic test.
• Adjuvant corticosteroids alongside antibiotics have trial evidence in children with septic arthritis (faster CRP normalisation, shorter antibiotic course), but there is not yet enough adult trial data to make a therapeutic recommendation (registry: bsr-hot-joint-update-2017; verified 2026-08-14).
• Crystal arthropathy (gout, pseudogout) is the main differential and can coexist with infection — a positive crystal finding on microscopy does not exclude septic arthritis if clinical suspicion remains.

Step 2: mimics of joint disease

Several non-articular conditions present with joint pain and should be excluded before assuming a primary rheumatic disease:

Condition	Sex	Age	Accompanying findings	Laboratory
Fibromyalgia	F>>M	30–55	Fatigue, sleep disturbance, cognitive symptoms, psychiatric symptoms, headache, paraesthesia	None
Osteoarthritis	F>M	>60	Pain worse with use, bony swelling, joint deformity (e.g. Heberden’s nodes)	None
Osteomalacia	F=M	any	Muscle weakness, spasms/cramps, difficulty walking, fracture	↑ALP, ↑PTH; ↓Ca, ↓P, ↓25-OH vitamin D
Thyroid dysfunction	F>M	30–55	Palpitations, sweating, weight loss, hair loss	Abnormal TSH/free T4
Hyperparathyroidism	F>M	>60	Weakness, fatigue, polyuria, polydipsia, osteoporosis	↑PTH, ↑Ca; ↓P
Hypermobility syndromes	F>M	<30	Recurrent subluxations, hyperextensible skin, bowel symptoms	None
Malignancy	F=M	any	Weight loss, fever, pain at rest and at night	Hypercalcaemia, ↑LDH, cytopenia

Step 3: pattern-recognition for true polyarthritis

Disease	<40y	40–60y	>60y	Female	Male	Pattern
Rheumatoid arthritis	+	+++	++	++	+	Small joints, symmetric, additive
Psoriatic arthritis	+++	+++	+	++	++	Small/large/axial joints, asymmetric, additive
Ankylosing spondylitis	+++	++	+	+	++	Large joints, axial, asymmetric, additive
Reactive arthritis	+++	++	+	++	++	Large joints, asymmetric, migratory
Crystal arthropathy	+	++	+++	++	+	Small joints, asymmetric, intermittent
Systemic lupus erythematosus	+++	++	+	++++	+	Small joints, symmetric, additive
Systemic vasculitis	++	+++	++	+++	++	Small joints, symmetric, additive

Table adapted from a PMC review of polyarticular joint pain.

Investigating suspected inflammatory joint disease: avoid the blanket “autoimmune screen”

It is tempting to order a combined ANA/ANCA/HLA-B27/ENA/dsDNA panel for any patient with arthralgia, fatigue or a non-specific rash — but this is not supported by the evidence and frequently causes harm through false positives.

• Without a suggestive history and examination, the pre-test probability of most of these diseases is low: RA ~1–2% of the population, SLE ~1:1000, and ANCA-associated vasculitis ~16:100,000. A positive ANA or ANCA in a patient without a compatible clinical picture is, far more often than not, a false positive.
• Neither non-inflammatory back pain, nodal osteoarthritis, isolated fatigue, nor widespread non-articular pain are — in isolation — manifestations of RA, SLE or ANCA-associated vasculitis, and testing for these conditions in that context will mostly generate spurious results requiring further (unnecessary) work-up.
• The Australian Rheumatology Association’s own EVOLVE “top five” recommendations advise against serological testing in patients with a low pre-test likelihood of SLE.
• Practical rule: request serology to confirm or refute a specific diagnosis you have already arrived at on clinical grounds — not as an undirected screening panel (registry: ajgp-autoimmune-screen-2019; verified 2026-07-23; quote: “Rheumatological diagnoses cannot be made purely by isolated test results that do not reflect the patient context.”).