Septic arthritis is a rheumatological emergency — proteolytic enzymes from neutrophils and bacteria damage cartilage, so delay worsens outcome. Staphylococcus aureus is the most common organism; streptococci, gonococci and gram-negative organisms also occur. A high synovial fluid white cell count supports infection but is not a diagnostic threshold (crystal arthritis can produce similar counts) — Gram stain and culture matter. Aspiration before antibiotics helps guide therapy where it can be done promptly, but antibiotics must not be delayed in a septic or unstable patient. Risk factors: prosthetic joint (a serious infection — local orthopaedic/microbiology pathway), IV drug use, immunosuppression, diabetes, skin disease (psoriasis creates skin barrier breaks), recent joint injection. Any prosthetic joint with pain + fever = surgical emergency.

The duration of morning stiffness is a useful clinical feature for distinguishing inflammatory from mechanical joint disease. Morning stiffness lasting more than 30 minutes suggests inflammatory pathology (RA, psoriatic, reactive) — it reflects the time required for synovial gel phenomenon to resolve as the joint warms with activity. OA morning stiffness is absent or lasts no longer than 30 minutes (NICE NG226). The older 1987 ACR criteria used stiffness of at least 1 hour; morning stiffness is not part of the ACR/EULAR 2010 RA classification criteria, and no stiffness threshold should delay referral of persistent synovitis. The second key distinction is the relationship of pain to activity: inflammatory arthritis characteristically worsens with inactivity and improves with movement (joints feel worse first thing in the morning and after sitting), while OA worsens with use (pain builds with sustained activity and relieves with rest). Patients often describe OA as "the more I do, the more it hurts" and inflammatory arthritis as "the more I rest, the stiffer I get."

The anti-CCP (anti-cyclic citrullinated peptide) antibody is a highly specific test for RA, but it is supportive rather than diagnostic and a negative result does not exclude RA. Positive anti-CCP in early inflammatory arthritis is highly predictive of RA development and is associated with more erosive, aggressive disease. A patient with anti-CCP positive symmetrical small joint polyarthritis and elevated CRP should be referred to rheumatology as a matter of urgency (NICE NG100: refer urgently; NICE QS33 — check local referral routes and targets). NICE NG100 asks for referral of any adult with suspected persistent synovitis of undetermined cause, and urgently even with a normal acute-phase response or negative RF/anti-CCP — so all patients with persistent joint swelling of unclear cause should be referred to rheumatology regardless of serology. Distinguishing RA from psoriatic arthritis is clinically important as they have different DMARD pathways — psoriatic arthritis often responds well to TNF inhibitors and IL-17 inhibitors, while methotrexate is the anchor DMARD for RA.

DAS28 (Disease Activity Score in 28 joints) is the validated clinical tool used by rheumatologists to monitor RA disease activity and guide DMARD dose escalation and treat-to-target decisions. It incorporates: 28-joint tender count, 28-joint swollen count, patient VAS (visual analogue scale for global health), and CRP (or ESR). DAS28 <2.6 = remission; 2.6–3.2 = low activity; 3.2–5.1 = moderate; >5.1 = high. NICE NG100 recommends treat-to-target, aiming for remission (DAS28 <2.6) or low disease activity if remission cannot be achieved, with CRP and disease activity measured monthly in specialist care until the target is reached. GPs who see patients on DMARDs should be familiar with DAS28 from rheumatology letters to understand disease activity status and treatment appropriateness.

The urgency of RA referral (NICE NG100: refer urgently; NICE QS33 sets referral standards — check local routes and targets) is based on evidence that treatment delay significantly worsens long-term joint damage outcomes — the window of opportunity for suppressing the immune cascade before erosive joint destruction occurs is narrow. Patients with RA who start DMARDs within 3 months of symptom onset have significantly better 5-year and 10-year functional outcomes than those starting later. The GP should not wait for repeat bloods or X-ray reports before referring — clinical suspicion of persistent synovitis is sufficient to refer urgently — normal inflammatory markers, negative serology or normal X-rays should not delay referral. The rheumatologist will arrange the further investigations. The most common cause of delayed RA diagnosis in primary care audit data is repeat GP consultations without progression to referral.

Starting DMARDs (methotrexate, hydroxychloroquine, sulfasalazine) in primary care before a rheumatological diagnosis is confirmed is inappropriate and potentially harmful. DMARDs require: tuberculosis screening (IGRA test — methotrexate reactivates latent TB), hepatitis B screening (methotrexate and biologics can reactivate HBV), DEXA scan baseline (steroid-sparing), full blood count and LFT baseline, and patient counselling about teratogenicity and monitoring requirements. These are rheumatologist-led investigations. The GP's role is symptomatic relief (NSAIDs after risk assessment; steroid only on specialist advice) while ensuring urgent rheumatology referral is made; DMARD initiation is normally rheumatology-led or within an agreed shared-care pathway. The risk of delaying DMARD initiation is real (joint erosion) but the risk of starting immunosuppression without proper screening is also significant.

Methotrexate pneumonitis (MTX-induced lung toxicity) is a rare but life-threatening complication — it presents as progressive dyspnoea, dry cough, and fever, typically within the first 12 months of treatment. Any patient on methotrexate who develops new breathlessness, dry cough or fever needs urgent clinical assessment, with methotrexate withheld and specialist advice sought. Methotrexate pneumonitis is rare but can be serious. New dyspnoea in an RA patient on methotrexate must never be attributed to infection or heart failure without specifically considering MTX lung toxicity. The GP's monitoring protocol is set by the BSR csDMARD guideline (2025, replacing BSR/BHPR 2017) and local shared-care agreements — failure to monitor and resulting MTX toxicity is a documented cause of GP negligence claims.

Exercise is the most evidence-based treatment for OA — multiple systematic reviews and meta-analyses demonstrate that land-based exercise reduces OA pain and improves function, with no ceiling effect across ages and severities. The key barrier is patient belief that exercise "wears out" the joint — this is scientifically incorrect and must be actively dispelled. Cartilage has no blood supply; it is nourished by the compressive-release pumping action of joint movement. Regular moderate exercise maintains cartilage health. Paracetamol has minimal evidence for OA pain — a 2016 Lancet meta-analysis of 74 trials found paracetamol had clinically insignificant effects on OA pain compared to placebo. NICE NG226 (2022) therefore advises against routinely offering paracetamol for OA. NSAIDs have better evidence but worse side effect profiles — use lowest effective dose for shortest duration.

The risk of septic arthritis in patients on biologic DMARDs (TNF inhibitors, JAK inhibitors) is higher than in the general population — these drugs suppress the innate and adaptive immune response that normally prevents haematogenous seeding. Any patient on a biologic who develops a hot, swollen, acutely painful joint should be considered to have septic arthritis until joint aspiration proves otherwise. This is clinically challenging because biologics also suppress the inflammatory features of gout and RA flares — leading to presentations where crystal arthritis or RA flare mimics septic arthritis. The answer in all cases is the same: urgent hospital assessment for joint aspiration and culture. GPs should have a low threshold to call rheumatology directly when managing joint flares in biologic-treated patients.