Calcium pyrophosphate dihydrate crystal deposition disease and pseudogout of the acromioclavicular joint: radiographic and pathologic features.

OBJECTIVE: To correlate the radiographic and pathologic findings in calcium pyrophosphate dihydrate (CPPD) crystal deposition disease and the pseudogout syndrome in the acromioclavicular (AC) joint, a relatively infrequent, but clinically important site.
METHODS: We describe a case with a definite diagnosis of CPPD crystal deposition leading to pseudogout of the AC joint. We also identified 17 other patients with CPPD crystal deposition disease who showed intraarticular or periarticular calcification in this joint and investigated the radiographic findings in 26 AC joints in these 17 patients. We then correlated the results with the pathologic findings in 2 cadavers with AC joint manifestations of the disease.
RESULTS: Intradiscal calcification, mainly linear or punctate in configuration, was found between adjacent bony margins in 9 of 26 AC joints (35%) or between the bony margins and extending above the upper articular bony margin in 14 AC joints (54%). Two joints (8%) showed diffuse calcification within the discs between, above, and below the articular bony margins. The remaining joint (3%) had intradiscal calcification only above the upper bony margins of the AC joint. All the joints with calcifications above the articular margins had associated globular or tumor-like soft tissue masses. A pseudogout attack at the AC joint may have nonspecific shoulder pain as its presenting symptom.
CONCLUSION: CPPD crystal deposition disease leading to pseudogout syndrome of the AC joint is a clinically significant condition. We emphasize that careful assessment of the AC joint and adjacent soft tissue using intensive bright light on routine shoulder radiographs may increase the sensitivity of detecting discal and capsular calcifications in patients with pseudogout of the shoulder.