Unusual presentation of nonhemophilic hemosiderotic synovitis mimicking pigmented villonodular synovitis in the left shoulder, a case report

a l P r e -p r o o f Non-hemophilic haemosiderotic synovitis (NHS) is a rare and incompletely understood pathological condition characterized by the accumulation of hemosiderin within the synovial lining of joints.This is typically a result of chronic intra-articular haemorrhage [5] and can lead to chronic inflammation, pain and stiffness [10].Haemosiderotic synovitis is seen most in the knee joint, although more commonly in haemophilic patients as a result of recurrent bleeding.Meanwhile, unlike these hemophilic pseudotumors, NHS occurs in patients without underlying coagulopathies.Its clinical and radiological findings bear similarity to pigmented villonodular synovitis (PVNS), making it difficult to distinguish the two.NHS has predominantly been observed in the knee, whilst the shoulder joint, a complex and highly mobile articulation, is an exceedingly rare site for NHS, making reported cases scarce in the literature.In addition, it poses significant diagnostic difficulty, as imaging features can closely overlap not only with PVNS, but also other intra-articular pathologies, such as rotator cuff tears, osteoarthritis or inflammatory arthropathies.This diagnostic ambiguity increases the risk of delayed recognition and inappropriate management, potentially resulting in progressive joint destruction and functional impairment.The authors report a case of a 50-year-old female patient with left shoulder NHS, who underwent arthroscopic resection of NHS with good pain relief and functional recovery at 1 year.