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Pseudogout — SCE Rheumatology MCQ

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ModerateCrystal ArthropathyPseudogoutSCE Rheumatology

A 72-year-old woman has recurrent, crystal-proven acute calcium pyrophosphate crystal arthritis. Investigations obtained while she is clinically stable show an albumin-adjusted calcium concentration of 2.85 mmol/L on two occasions (reference range 2.20–2.60), parathyroid hormone 12 pmol/L (reference range 1.6–6.9), phosphate 0.65 mmol/L (reference range 0.80–1.50), and eGFR 78 mL/min/1.73 m². Which metabolic disorder associated with CPPD is most strongly indicated by these findings?

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Correct answer: E — Primary hyperparathyroidism

The correct answer is primary hyperparathyroidism. Repeated hypercalcaemia with an inappropriately elevated PTH indicates PTH-dependent hypercalcaemia; the accompanying hypophosphataemia and preserved renal function further support primary rather than tertiary hyperparathyroidism. Primary hyperparathyroidism is a recognised metabolic disorder predisposing to CPPD. Haemochromatosis, hypomagnesaemia and hypophosphatasia are also genuine CPPD associations, making them plausible distractors, but none explains this biochemical pattern. Hypothyroidism has historically been reported with chondrocalcinosis, but the association is less firmly established and it would not produce PTH-dependent hypercalcaemia. The associated metabolic disorder should be assessed and treated on its own merits, although correction does not reliably reverse established CPP crystal deposition.

Reference: Abhishek A et al. The 2023 ACR/EULAR classification criteria for calcium pyrophosphate deposition disease. Annals of the Rheumatic Diseases. 2023;82:1248–1257. https://www.nice.org.uk/guidance/ng132/chapter/Recommendations