Frozen shoulder: a sympathetic dystrophy? 
Diagnostic and clinical features of the frozen shoulder syndrome and the Sudeck syndrome are similar in many aspects.  Radioisotope bone scan shows an increased uptake in affected areas in both diseases, while native radiographs show a progressive demineralisation.  Measurement of bone mineral density (BMD) by quantitative digital radiography objectified these local decalcification processes in an early stage of the frozen shoulder syndrome; 10 of 12 patients with primary frozen shoulder had BMD decreases greater 21% in the humeral head of the affected shoulder compared to the non-affected side.  In the immobilised control group with degenerative changes of the rotator cuff, calcifying tendinitis and shoulder instability (n = 12) and in the group of healthy probands (n = 20), the difference between the affected and non-affected side (left and right humerus of the healthy probands) was only more than 21% in one case each.  There are several references in the literature that assume frozen shoulder to be an algoneurodystrophic process; our observations support this hypothesis, possibly leading to earlier diagnoses and extended therapeutic management.