Introduction: Rheumatoid arthritis (RA) patients are at increased risk of developing septic arthritis. Factors that contribute to this risk include immunosuppressive drugs, joint aspiration and corticosteroid injections etc. As septic arthritis is associated with increased mortality and morbidity, naturally index of suspicion for septic arthritis in RA patients is high, when these patients present with acute hot joints. However, septic arthritis is not the only cause of acute hot joint and we need to look beyond the involved hot joint for answers.
Case description: We report a case of 85 years old Caucasian female with about 20 year history of seropositive RA on Methotrexate and Sulfasalazine since diagnosis. She was admitted via accident and emergency department with 1 week history of feeling unwell. She reported fever and right right hip and low back pain. She was unable to weight bear due to painful right hip. She had a temperature of 38 degrees recorded by ambulance crew. On further enquiry, she reported some right ankle and left knee pain She looked unwell and was distressed due to painful right hip. Observation at admission: Temperature: 37.7 °C, Blood pressure: 148/60 mmHg, Heart rate bpm: 84 beats per minute, Respiratory rate: 15 per minute, Oxygen saturation: 96% on room air On musculoskeletal examination: Right hip was severely tender on both active and passive slightest movements; and she was struggling to weight bear on the right hip. She was tender over the sacrum with no superficial erythema or swelling noted. Spinal assessment was limited but there was no obvious tenderness over the lumbar region – vertebral discs and paravertebral area. Left knee examination identified small effusion at the left knee. There was tenderness on left ankle but there was no synovitis or effusion. Systemic review was unremarkable. Investigations revealed stable renal function, anemia of chronic disease (Haemoglobin 102g/l(115-165), Mean Corpuscular Volume 94Fl(84-105)), White Cell Count 8.1/litre(4 – 11), Neutrophils 6.5/litre(1.8 – 7.5), Platelets 344/litre(150 – 450), Liver function test – normal. Inflammatory markers revealed markedly elevated CRP 233 mg/l(0-10) and ESR 95mm/hour. These markers were normal at recent clinic assessments. Uric acid level was 298 µmol/l. Bone profile, phosphate and magnesium were all normal. Chest x-rays was clear, urine dipstick was normal, multiple blood cultures were taken on admission. X-rays right hip and left knee showed mild to moderate degenerative changes and no evidence of chondrocalcinosis. Our working diagnosis at this stage was right hip septic arthritis and discitis. We therefore proceeded with an urgent MRI scan of hip and spine. An urgent orthopaedic opinion was requested with view for right hip aspiration and wash for suspected septic arthritis. We withheld both her disease modifying anti-rheumatoid drugs. On- call microbiology consultant advised withholding antibiotics until joint aspiration as patient was hemodynamically stable. She has been given oral morphine for pain control. We proceeded with left knee joint aspiration as that was the only accessible joint to aspiration without image guidance. Left knee aspirate was clear and straw coloured. This was sent for microscopy, crystallography and cultures. The local synovial fluid analysis did not identify organisms or crystals. Later that day, MRI scan right hip confirmed large right hip effusion. MRI lumbosacral spine did not suggest features of spinal abscess or discitis. Orthopaedic surgeons review her that day and listed her for right hip aspiration in the operating theatre next morning. Senior orthopaedic hip surgeon reviewed the patient next morning by which point patient had improved significantly and was able to weight bear. The hip surgeon then felt that this is unlikely septic arthritis and decided not to proceed with the previously planned arthroscopy. We still felt that sepsis needed to be excluded in view of a large hip effusion on MRI and a marked inflammatory response. An urgent ultrasound guided right hip aspiration was arranged. However, USS done pre aspiration confirmed that the right hip effusion had resolved completely at 48 hours. This lady continued to make good clinical progress. Blood and urine cultures result were all negative. We felt the acute right hip symptoms may have been an acute RA flare. Interestingly, detailed synovial fluid analysis became subsequently available and confirmed calcium pyrophosphate crystals. This is the full result: Rhagocytes 0%, Crystals Calcium pyrophosphate, Other Fibrin, WBC 4900 WBC/cu mm(WBC/cu mm < 1000 = non inflammatory, =/>1000 = inflammatory) We believe the right hip symptoms are more compatible with an episode of acute pseudogout and are supported by identification of calcium pyrophosphate crystals in synovial fluid of other less symptomatic joint. Ideally the symptomatic joint aspirate would settle this issue but that could not be achieved in our patient. This patient had not received any antibiotics, corticosteroid or NSAIDs in addition to the opiate analgesia during her hospital stay. She improved back to her baseline and was discharged to be followed up in 8 weeks.
Discussion: This case demonstrates the importance of aspirating seemingly quiescent joints in patients who present with suspected septic arthritis or there mimics as these joints may not always be amenable to aspiration. Imaging the affected joint does not give a definite diagnosis either. Chondrocalcinosis – calcification of cartilage identified on radiographs prompts clinicians to consider CPPD disease as a potential cause but is not diagnostic. In about 40% of patients with crystallography proven pseudogout, the radiographs may not identify chondrocalcinosis. Also, CPPD is not the only crystal that leads to chondrocalcinosis. X-rays are not usually helpful as chondrocalcinosis in the joint spaces may only be present in about 40% of the cases(1) RA is rarely reported to be associated with pseudogout. Alhadad et al (2) showed that 8 patients amongst 62 patients with pseudogout were found to have RA They also noted that there is associated increased severity of attack in patients with background inflammatory arthritis such as RA. However, the study was not powered to be of statistical significance. In our patient, the identification of associated CPPD disease will be helpful for long term management. If CPPD was not identified, future flares could be attributed to RA flare leading to unwarranted changes in RA therapy. Low dose Prednisolone would be a potential option in this elderly lady with RA should she experience further episodes of pseudogout as it will help both RA and pseudogout flares. This is a rare clinical case of acute pseudogout in an elderly RA patient which mimicked septic arthritis.
Key learning points: Synovial fluid analysis and culture of synovial aspirate from less symptomatic joint can be valuable in patients with acute hot joints which may not be readily accessible for aspiration. Absence of chondrocalcinosis does not exclude the diagnosis of pseudogout.