Resident Mary Free Bed Hospital PM&R Program Grand Rapids, Michigan
Case Diagnosis: Hydroxyapatite Deposition Disease vs. Heterotopic Ossification in patient with knee pain
Case Description or Program Description: 33 year old male admitted to Inpatient Rehabilitation (IPR) for multifocal stroke with right sided hemiparesis. On day one, patient reported insidious, right knee pain without history of trauma. Pain was described as sharp and localized to superomedial knee.
Setting: Acute Inpatient, Rehabilitation Hospital
Assessment/Results: Physical exam demonstrated palpable mass, erythema and tenderness at the distal attachment of the vastus medialis. Knee flexion was limited by pain. Radiograph demonstrated calcifications on the medial aspect of the supracondylar region extending down to the medial margin of the femoral condyle. MRI demonstrated small joint effusion and small, hypoechoic regions adjacent to femoral condyle with surrounding soft tissue edema. Alkaline phosphatase was unremarkable. Inflammatory markers were mildly elevated. Infectious work up remarkable for known, controlled HIV positive status. With gentle range of motion exercises, the pain spontaneously resolved within a week.
Discussion (relevance): Hydroxyapatite Deposition Disease (HADD) is the formation of Hydroxyapatite crystals near tendon attachments and joint capsules. Pathology is unknown and it can be challenging to differentiate from Heterotopic Ossification (HO). Gold standard diagnostic approach would be Calcium Pyrophosphate Crystals on joint aspiration. However, this patient’s pain spontaneously resolved and aspiration and was felt to pose higher risk than benefit. Additional findings supportive of HADD in this case are unremarkable alkaline phosphatase (not affected in HADD, though may be elevated in HO), location of calcification (commonly along femoral condyle in HADD) and self-resolution of symptoms. Although possible that this is early HO, spontaneous resolution of symptoms would be atypical. HADD is often treated with steroids and differs from HO in that symptoms can resolve within weeks without treatment.
Conclusions: This case elucidates the clinical challenge of differentiating between HADD and HO with brief discussion of the differences in treatment and prognosis.