E026 Hypertrophic pulmonary osteoarthropathy, rheumatoid arthritis mimic: don’t distract with immunology
Authors: Awan Abdul B , Javaid Farhan , Moorthy Arumugam , Sunmboye Kehinde 
Published: April 2023

Abstract

Background/Aims
Hypertrophic pulmonary osteoarthropathy is a para-neoplastic syndrome characterized by periosteal bone proliferation, clubbing, swelling of soft tissues and joints which is frequently associated with adenocarcinoma of lung. We hereby present a case series of two very interesting cases who were initially thought to have seropositive inflammatory arthritis, but later on investigation confirmed an underlying lung malignancy-associated secondary hypertrophic pulmonary osteoarthropathy.

Methods
Case 1:A 62-year-old female with previous history of leucoclastic vasculitis and hypertension, presented to rheumatology with 6 months history of widespread polyarthralgia associated with prolonged early morning stiffness. She had been smoking 10 cigarettes a day for 30 years. Clinical examination revealed no synovitis or restriction of joint movements. C-reactive protein was raised, rheumatoid factor was 284 (Normal 0-15), anti-CCP antibodies were 1 (0-6). She was diagnosed of inflammatory arthritis and started on hydroxychloroquine, with no response. Review at 4 months confirmed new swelling over the fingertips associated with weight loss, loss of appetite and persistent mild cough. Examination confirmed tenderness over the distal radius and proximal tibia with pronounced grade 3 to 4 clubbing in fingers and toes, no clinically detectable active synovitis noted. CT scan showed a large left upper lobe mass, and spinal metastases and biopsy confirmed adenocarcinoma.

Results
Case 2: A 74-year-old gentleman with 50 pack year history of smoking and past medical history of paroxysmal atrial fibrillation, peripheral vascular disease and Type 2 diabetes mellitus, initially presented with 10 months history of constant pain only in left big toe joint, associated with significant weight loss and on-going shortness of breath for past few months. Investigations revealed rheumatoid factor 1300 (0-15) and anti-CCP antibodies &gt;340 (0-6), C-reactive protein was 54. On examination digital clubbing was noted, no synovitis or restriction of joint movements. Chest X-ray demonstrated right middle zone mass. CT Thorax abdomen & pelvis confirmed malignancy.

Conclusion
Rheumatoid Factor has a pooled sensitivity of 69% and a specificity of 85%. Sensitivity and specificity of anti-CCP antibodies are 66% and 90.4%, respectively. Both are useful in the diagnosis of rheumatoid arthritis, but can be false positive, and can sometimes be misleading. Studies have shown a direct relation between rheumatoid factor, anti-CCP antibodies and smoking. Titres were significantly higher in heavy smokers. This case series reminds us that hypertrophic pulmonary osteoarthropathy can mimic rheumatoid arthritis. Where clinical features are not convincing of inflammatory arthritis, and red flags like history of smoking and digital clubbing are present, a high index of suspicion is required to rule out a paraneoplastic condition.
Disclosure
A.B. Awan: None. F. Javaid: None. A. Moorthy: None. K. Sunmboye: None.