Joint Pain OSCE - Reactive Arthritis

Case Overview

• Age/Sex: 26-year-old male
• Occupation: Personal trainer / fitness instructor
• Setting: Primary care / urgent clinic
• Chief complaint: "Painful joints"

Patient Script

Who I Am

I'm 26, I work as a personal trainer at a local gym and I'm pretty active most days.

What Brings Me In

My knees and ankles have been painful and swollen for the past week and it's getting in the way of work.

My Story

About three weeks ago I had a bout of stomach upset — I had diarrhoea for about four days after a takeout meal. I thought it was food poisoning and it settled down. About ten days ago I had a bit of burning when I peed for a day or two but there wasn't much discharge and I didn't see a doctor. Then one week ago I started getting a painful, swollen left knee and a sore right ankle. The pain is worse when I run or when I get up from sitting, and the knee is visibly swollen. Two days ago I noticed my left eye was red and a bit gritty but it's not very painful. I haven't had anything like this before.

I also sprained the same ankle a couple of months ago playing football, but that had mostly recovered. I go climbing sometimes and I took a protein supplement this month. I had a one-night stand about five weeks ago and used a condom most of the time — I can't be 100% sure there wasn't exposure.

My Medical Background

• Past medical history: none significant; no previous arthritis
• Medications: occasional ibuprofen for pain, protein/creatine supplement
• Allergies: none known
• Social: non-smoker, drinks alcohol socially (weekend beers), sexually active with multiple partners in the past year, uses condoms most of the time
• Recreational drugs: tried cocaine once several months ago (single event)
• Family history: no autoimmune disease, no gout

What I Think & Worry About

• I think it might be some kind of arthritis and I'm worried I won't be able to work or train clients.
• I'm anxious it could be a sexually transmitted infection or something that will affect my fertility.
• I worry it could be something serious like an infection in the joint.

If You Ask Me About Other Symptoms...

• Fever: I felt a bit feverish during the diarrhoea episode but haven't measured a temperature since.
• Skin: No rashes on my arms or face; I noticed a small hard spot on the sole of my foot after football last week (I thought it was a callus).
• Eyes: My left eye is red and gritty, no pus, no blurring of vision.
• Genitourinary: Burning on passing urine for a day or two 10 days ago, resolved on its own; no current discharge or ongoing pain.
• Bowel: diarrhoea 3 weeks ago for four days; since then normal stools.
• Recent travel: none of significance; no camping except a day hike two months ago (no known tick bite).
• Prior joint problems: just the ankle sprain months ago which settled; no chronic stiffness in the morning beyond a few minutes.

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Clinical Summary

Examination

• General: well-looking, afebrile in clinic (T 37.2°C), BMI 24
• Cardiovascular: heart sounds normal, no murmurs
• Respiratory: clear
• Left knee: warm, effusion present, reduced range of motion, tenderness on medial joint line, difficulty weightbearing on that leg
• Right ankle: mild swelling, tenderness over lateral malleolus and Achilles insertion, pain on dorsiflexion
• Small joints of hands: mild ache on active use but no synovitis or deformity
• Eyes: left conjunctival injection, no discharge, visual acuity intact
• Genital/urethral: no active discharge, mild meatal erythema
• Skin: single hyperkeratotic papule on plantar surface (possible callus); no psoriatic plaques

Investigations

• CBC: WBC 9.8 x10^9/L (normal), Hb 145 g/L, Platelets 280 x10^9/L
• CRP: 28 mg/L (elevated)
• ESR: 30 mm/hr (elevated)
• Serum uric acid: 350 µmol/L (within normal range for lab)
• Knee joint aspiration: synovial fluid WBC 25,000/mm3, 80% neutrophils (inflammatory); Gram stain negative; culture negative at 48h (pending final) (supports sterile inflammatory arthritis)
• X-ray left knee/right ankle: soft tissue swelling, no erosions or joint space narrowing
• Urine dip: leukocyte esterase positive, nitrite negative
• Urine NAAT for Chlamydia trachomatis/Gonorrhoea: Chlamydia trachomatis NAAT positive (supports preceding GU infection)
• HLA-B27: positive (increases likelihood/severity of reactive arthritis)

Diagnosis

Primary: Reactive arthritis (post-infectious oligoarthritis) likely triggered by Chlamydia trachomatis infection.

• Evidence: recent diarrhoeal illness and transient dysuria 1–3 weeks prior to onset of asymmetric oligoarthritis affecting lower limbs; conjunctival irritation; sterile inflammatory synovial fluid; positive Chlamydia NAAT; HLA-B27 positive.

Differentials:

• Septic arthritis: considered given knee effusion, but synovial fluid gram stain and culture are negative and systemic features absent, making septic arthritis unlikely but should be monitored until cultures finalize.
• Crystal arthropathy (gout/pseudogout): less likely given age, distribution, normal serum uric acid and inflammatory synovial fluid without crystals on microscopy.
• Rheumatoid arthritis: unlikely — presentation is asymmetric oligoarthritis predominantly lower limb, lack of chronic symmetric small joint involvement, negative RF/CCP not supportive.
• Psoriatic arthritis: less likely — no personal or family history of psoriasis, no psoriatic skin or nail changes.
• Lyme disease: possible red herring from hiking history but no erythema migrans, timing and NAAT positive for Chlamydia point away from Lyme.

Management

• Immediate:
  • Start NSAID therapy (e.g., naproxen) for pain and inflammation unless contraindicated.
  • Aspirate the knee for symptomatic relief (already performed) and send fluid for culture and crystals — continue to observe while cultures pending.
  • Start appropriate antibiotic therapy for Chlamydia trachomatis (e.g., doxycycline 100 mg PO twice daily for 7 days) and arrange sexual health clinic referral; advise partner notification and testing.
• Symptom-specific:
  • Consider a single intra-articular corticosteroid injection for the knee if pain remains limiting after aspiration and infection adequately excluded.
  • Manage conjunctivitis supportively; if symptoms worsen, refer to ophthalmology.
  • Physiotherapy referral for mobility, strengthening, and return-to-play advice.
• Follow-up and escalation:
  • Review in 1–2 weeks to assess response; if persistent or progressive arthritis, consider rheumatology referral and disease-modifying therapy (e.g., sulfasalazine) if chronic.
  • If synovial fluid cultures become positive or patient develops systemic signs (fever, worsening pain), escalate for admission and intravenous antibiotics for possible septic arthritis.

Key Learning Points

• Reactive arthritis commonly follows a urogenital or gastrointestinal infection by 1–4 weeks and often presents as an asymmetric oligoarthritis of the lower limbs, sometimes with conjunctivitis and urethritis.

• Joint aspiration is essential to exclude septic arthritis; reactive arthritis typically shows an inflammatory but sterile synovial fluid.

• Management includes treating the triggering infection (if identified), symptomatic control with NSAIDs and physiotherapy, sexual health measures, and rheumatology follow-up if symptoms persist or become chronic.