Abstract Background/Aims Atraumatic arthritis is frequently seen in unplanned care environments. This case highlights a rare cause of joint pain in younger people and hints at a possible unrecognised association with HIV or its treatment. Methods A 36-year-old male presented with nine days of pain and swelling of the left ankle. He had no similar previous episodes, no preceding illnesses, no recent travel, no new or high-risk sexual encounters, no trauma, and no other new symptoms. Past medical history was remarkable only for HIV infection diagnosed in 2013, stably undetectable on antiretroviral therapy with Stribild once daily. No other relevant medical or family history was obtained, and a recent GUM screen was negative. The patient reported occasional alcohol use, and no smoking or substance use. BMI was 30. Observations were unremarkable and the patient apyrexial. On examination, he had an antalgic gait, reduced range of motion of the left ankle, and a clinically evident effusion. Bedside ultrasound confirmed a tibiotalar effusion. Examination was otherwise normal. An aspirate was sent for culture and sensitivity. Surprisingly, microscopy revealed calcium pyrophosphate crystals. No organisms were seen on gram staining, and enrichment culture was negative. A diagnosis of CPPD was made. The patient was treated with a seven-day course of 20mg oral prednisolone and advised to discontinue ibuprofen due to the interaction with his antiretroviral therapy. Results CPPD can be categorised as hereditary, idiopathic or secondary. A hereditary cause cannot be excluded, although there was no known family history. Idiopathic presentation usually affects middle-aged to elderly patients, so a case of pseudogout in a young patient warrants further investigation. Secondary causes of CPPD include disturbances of bone metabolism such as hyperparathyroidism, hypercalcaemia, and hypophosphataemia. Abnormal iron or copper handling can also lead to the condition, as can thyroid dysregulation. Our patient is not known to suffer from any of these conditions. Studies have shown a link between HIV, or its antiretroviral treatment, and hyperparathyroidism, hypercalcaemia, hypophosphatemia, and hypothyroidism. It could be expected, given this overlap with the aforementioned secondary causes, that increased incidence of CPPD would be seen in HIV patients, but this is not a recognised association at present. 30-40% of HIV patients are documented as suffering from arthralgia, most commonly in their knees, shoulders, or elbows, but which can affect any joint. The aetiology of these symptoms is unclear, although it is known that HIV patients are at increased risk of gout, particularly when using ritonavir. Conclusion Given that crystal arthritis diagnoses are often made without the gold standard test of crystal microscopy, this raises the question of whether CPPD is being underdiagnosed in this otherwise unusual demographic, and could be responsible for more morbidity here than is currently recognised. Disclosure S. Langdon: None. E. Wheatley: None. C. Chown: None. J.A.W. Mogg: None.
Langdon et al. (Wed,) studied this question.