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Milwaukee shoulder syndrome (basic calcium phosphate crystal-associated destructive arthropathy) — SCE Rheumat

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ModerateSynovial Fluid AnalysisMilwaukee shoulder syndrome (basic calcium phosphate crystal-associated destructive arthropathy)SCE Rheumatology

An 82-year-old woman presents with recurrent atraumatic swelling of her dominant shoulder and progressively restricted movement. She has no fever and reports relatively modest pain despite marked functional impairment. Examination shows a large glenohumeral effusion, crepitus and profound weakness of abduction. Radiographs demonstrate superior migration and remodelling of the humeral head, advanced glenohumeral destruction and periarticular calcific debris. Ultrasonography confirms a massive chronic rotator-cuff tear. Her C-reactive protein is 7 mg/L and renal function is normal. Aspiration yields 55 mL of blood-stained fluid containing 650 leucocytes/mm³. Gram stain and culture are negative. Initial compensated polarised light microscopy identifies no birefringent crystals. Which additional synovial-fluid finding would most strongly support the suspected crystal-associated mechanism of this destructive arthropathy?

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Correct answer: D — Amorphous calcium-containing aggregates staining with alizarin red S

The combination of an elderly woman, a massive rotator-cuff defect, disproportionate glenohumeral destruction and a large blood-stained but non-inflammatory effusion is characteristic of Milwaukee shoulder syndrome, a basic calcium phosphate (BCP) crystal-associated destructive arthropathy. BCP crystals are submicroscopic and non-birefringent, so a negative routine compensated polarised examination does not exclude them. Amorphous calcium-containing aggregates may be demonstrated using alizarin red S, although this is a supportive rather than fully specific test and specialist analytical methods may be required for definitive characterisation. A describes monosodium urate crystals and would support gout. C describes calcium pyrophosphate crystals; CPP deposition can coexist with destructive arthropathy but does not best explain this classic cuff-tear phenotype. D describes cholesterol crystals, which may occur in longstanding effusions, particularly in chronic inflammatory arthritis, but are not the characteristic pathogenic deposit here. E describes calcium oxalate crystals, principally associated with advanced renal failure or primary hyperoxaluria; her normal renal function and characteristic shoulder imaging make this substantially less likely.

Reference: Milwaukee shoulder syndrome (2014) — https://pubmed.ncbi.nlm.nih.gov/24551470/ A Quantitative Spectrophotometric Assay Matched With Environmental Scanning Electron Microscopy to Measure Calcium Crystals in Human Osteoarthritic Synovial Fluid (2025) — https://pubmed.ncbi.nlm.nih.gov/41230552/ Detection of crystals in synovial fluids by light microscopy: sensitivity and reliability (1989) — https://pubmed.ncbi.nlm.nih.gov/2478085/