Positive Alizarin Red Clumps in Milwaukee Shoulder Syndrome

Abstract

To the Editor: Milwaukee shoulder syndrome is a destructive, basic calcium phosphate crystalline arthropathy characterized by pain, large-joint effusion, and loss of function in the affected joint1. It classically affects those over 70 years of age, 90% of whom are female. The syndrome is often associated with rotator cuff defects, and the effusion is noninflammatory with numerous aggregates of calcium hydroxyapatite crystals in the synovial fluid. Identifying individual calcium hydroxyapatite crystals in synovial fluid can be elusive, since these crystals are not identified under plain and polarized microscopy, unlike monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) crystals. However, globular clumps of hydroxyapatite crystals may appear using plain light microscopy, but they are not birefringent. Such clumps have been described as “shiny coins,” although often they either are … Address correspondence to Dr. C.J. Forster; E-mail: christopher.forster{at}us.army.mil