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OR5.1 | Inflammatory Arthritis — PBL Case

CLINICAL SETTING

Mr. Arjun Mehta, a 34-year-old secondary school teacher, presents to the orthopaedic outpatient department with a 10-month history of bilateral hand pain and swelling, making it difficult to grip chalk or write on the whiteboard. He describes significant morning stiffness lasting nearly 2 hours that improves once he begins his teaching rounds. He also reports lower back pain and stiffness that is worse at rest and at night, but reduces with movement. He has noticed a scaly skin rash over his elbows and scalp for the past 3 years, which he has largely ignored. On examination, there is bilateral swelling of the MCP and PIP joints of both hands, with the right index and middle fingers showing fusiform 'sausage-like' swelling encompassing the MCP, PIP, and DIP joints. The right DIP joint of the index finger appears erythematous and tender. There is tenderness over the right Achilles tendon insertion and over the right plantar fascia. Vital signs are normal. He is anxious about his ability to continue working.

Trigger 1: Initial Presentation and Differential Diagnosis

Routine blood tests reveal: ESR 62 mm/hr (normal <20), CRP 32 mg/L (normal <6), full blood count shows normocytic normochromic anaemia (Hb 10.8 g/dL). Rheumatoid factor: NEGATIVE. Anti-CCP antibodies: NEGATIVE. Uric acid: 4.8 mg/dL (normal). Liver and renal function: normal. X-rays of both hands (PA view) show soft tissue swelling around MCP and DIP joints of the right index finger; early erosion at the right index DIP joint with subtle widening of the joint space proximally.

DISCUSSION POINTS

  • Based on the history and these initial results, what is your primary diagnosis and why? What features of the history distinguish this from seronegative rheumatoid arthritis?
  • The RF and anti-CCP are both negative. Does this exclude rheumatoid arthritis? What seronegative inflammatory arthritis should be highest on your differential and why?
  • What is the significance of the 'sausage digit' (dactylitis) clinically? Which structures are inflamed in dactylitis?
  • Explain the pathophysiology of anaemia of chronic disease in this context — why is the ferritin elevated rather than low?
Click to reveal Trigger 2: Confirmatory Investigations and Diagnosis (discuss previous trigger first!)

Trigger 2: Confirmatory Investigations and Diagnosis

HLA-B27 testing returns POSITIVE. Pelvic X-ray shows bilateral sacroiliac joint blurring with early sclerosis at the iliac side, consistent with grade 2 sacroiliitis. MRI of the sacroiliac joints confirms active bilateral sacroiliitis with bone marrow oedema. The dermatology team reviews the skin lesions and confirms plaque psoriasis. X-ray of the right index finger now shows the characteristic 'pencil-in-cup' deformity at the DIP joint. The working diagnosis is established.

DISCUSSION POINTS

  • With the new investigation results, confirm the diagnosis. What are the five classical patterns of joint involvement in this condition?
  • Explain the 'pencil-in-cup' deformity radiologically — which bone is being eroded and what is the mechanical consequence?
  • HLA-B27 is positive. What is its clinical significance in this condition compared to its significance in ankylosing spondylitis? Is it diagnostic?
  • How would you distinguish this patient's axial symptoms from those of classic ankylosing spondylitis? What features overlap and what features are different?
  • What extra-articular manifestations would you actively screen for in this patient?
Click to reveal Trigger 3: Management Plan and Long-term Counselling (discuss previous trigger first!)

Trigger 3: Management Plan and Long-term Counselling

The patient is diagnosed with psoriatic arthritis (polyarticular pattern with axial involvement and dactylitis). He is started on naproxen 500 mg twice daily for symptom control and referred to rheumatology. The rheumatologist initiates methotrexate 15 mg once weekly with folic acid 5 mg once weekly (not on the same day), along with physiotherapy. After 6 months, the patient has improved but still has 2 swollen joints and ongoing axial symptoms. His school principal has asked for a medical report on his fitness to work.

DISCUSSION POINTS

  • What are the monitoring requirements for methotrexate therapy? What serious adverse effects must be watched for (pulmonary, hepatic, haematological)?
  • After 6 months of methotrexate with incomplete response, what is the next step in the management escalation ladder for this patient?
  • What counselling would you provide to Mr. Mehta regarding: (a) physical activity and joint protection at work, (b) long-term prognosis, (c) the importance of medication adherence, and (d) the risk of eye complications requiring ophthalmological review?
  • Draft key points for the medical fitness-to-work report for his school principal, explaining the condition in layperson terms and recommending workplace adaptations.

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [OR5.1] What are the clinical, serological, and radiological features that distinguish psoriatic arthritis from rheumatoid arthritis and from ankylosing spondylitis?
  2. [OR5.1] What is the pathophysiology of dactylitis and enthesitis in psoriatic arthritis, and which cytokines are primarily responsible for the joint inflammation?
  3. [OR5.1] What is the step-wise pharmacological management of psoriatic arthritis, from NSAIDs to csDMARDs to biologics, with specific drug names and monitoring requirements?
  4. [OR5.1] How is inflammatory arthritis distinguished from osteoarthritis clinically (history, examination, investigations, X-ray features)?
  5. [OR5.1] What are the extra-articular manifestations of rheumatoid arthritis (cardiovascular, pulmonary, ocular, haematological) and how are they screened for and managed?