An 80-year-old woman presents to her general practitioner (GP) with pain and swelling in her left knee. The pain began 2 days previously and she says that the knee is now hot, swollen and painful on movement. In the past she has a history of mild osteoarthritis of the hips. She has occasional heartburn and indigestion. She had a health check 6 months previously and was told that everything was fine except for some elevation of her blood pressure which was 172/102mmHg and her creatinine level, which was around the upper limit of normal. The blood pressure was checked several times over the next 4 weeks and found to be persistently elevated and she was started on treatment with 2.5mg bendrofluamethizide. The last blood pressure reading was 138/84mmHg. There is no relevant family history. She has never smoked and her alcohol consumption averages four units per week. She takes occasional paracetamol for hip pain.
Examination Her blood pressure is 142/86mmHg. The temperature is 37.5°C and the pulse 88/min. There is grade 2 hypertensive retinopathy. There is no other abnormality on cardiovascular or respiratory examination. In the hands there are Heberden’s nodes over the distal interphalangeal joints.
The left knee is hot and swollen with evidence of effusion in the joint with a positive patellar tap. There is pain on flexion beyond 90 degrees. The right knee appears normal.
Normal Haemoglobin 12.1g/dL 11.7–15.7g/dL White cell count 12.4 109/L 3.5–11.0 109/L Platelets 384 109/L 150–440 109/L Erythrocyte sedimentation rate (ESR) 48mm/h 10mm/h Sodium 136mmol/L 135–145mmol/L Potassium 3.6mmol/L 3.5–5.0mmol/L Urea 7.3mmol/L 2.5–6.7mmol/L Creatinine 116amol/L 70–120amol/L Glucose 10.8mmol/L 4.0–6.0mmol/L
ANSWER
The clinical picture is one of acute monoarthritis. The patient has a history of some hip pains but this and the Heberden’s nodes are common findings in an 80-year-old woman, related to osteoarthritis. The blood results show a raised white cell count and ESR, a raised blood sugar, and renal function at the upper limit of normal.
The differential diagnosis includes trauma, septic arthritis, gout and pseudogout. Differential diagnoses of pain in the knee
The recent introduction of a thiazide diuretic for treatment of the hypertension increases the suspicion of gout. Pseudogout is caused by deposition of calcium pyrophosphate crystals and would be expected to show calcification in the articular cartilage in the knee joint. The X-rays here show some joint space narrowing but no calcification in the articular cartilage. The fever, high white cell count and ESR are compatible with acute gout. The raised glucose may also be a side-effect of thiazide diuretics. If this remains after the acute arthritis has subsided then it may need further treatment. Precipitation of gout by thiazides is more likely in older women, particularly in the presence of renal impairment and diabetes. It may involve the hands, be polyarticular and can affect existing Heberden’s nodes. The serum uric acid level is likely to be raised, but this occurs commonly without evidence of acute gout. The definitive investigation is aspiration of the joint. The fluid should be sent for culture and inspection for crystals. A high white cell count would be expected in an acute inflammatory arthritis. The diagnosis is made from the needle-like crystals of uric acid which are negatively birefringent under polarized light, unlike the positively birefringent crystals of calcium pyrophosphate. In this case the pain in the joint was partly relieved by the aspiration. Treatment with a non-steroidal anti-inflammatory drug should be covered by a proton pump inhibitor in view of her history of heartburn and indigestion. The thiazide diuretic was changed to an angiotensin-converting enzyme inhibitor as treatment for her hypertension, and the blood glucose settled.