Calcific Periarthritis & Hydroxyapatite Deposition Disease (HADD)

A sudden, very painful, hot, swollen shoulder with an amorphous, cloud-like calcific deposit in the supraspinatus is an acute calcific periarthritis attack due to hydroxyapatite crystal deposition disease - the deposition of basic calcium phosphate crystals in periarticular soft tissue, here as calcific tendinopathy of the rotator cuff. The acute attack typically occurs during the resorptive phase, as the deposit is being resorbed, and it produces an intensely inflammatory picture that mimics septic arthritis and crystal arthritis such as gout. The key diagnostic point is that the hydroxyapatite crystals are too small to be seen on standard polarised microscopy, unlike the negatively birefringent needle-shaped urate of gout or the positively birefringent rhomboid crystals of CPPD, so the diagnosis is made on the imaging appearance of amorphous periarticular calcification rather than on crystal identification, and the attack is self-limiting over days to weeks. Where sepsis is a genuine concern I would exclude it with aspiration and cultures. Management is largely conservative: NSAIDs and rest for the self-limiting attack, with a subacromial corticosteroid injection if needed, and physiotherapy for chronic calcific tendinopathy. For a refractory deposit I would use ultrasound-guided barbotage - needle aspiration and lavage of the calcium - which is an effective minimally invasive first-line procedure, with extracorporeal shockwave therapy as an alternative and surgical removal reserved for the few that fail. I would also remember the destructive variant, Milwaukee shoulder, and that a deposit in a confined space such as the carpal tunnel can cause a compressive neuropathy.