BACKGROUND: It was reported that some shoulder tumors were misdiagnosed with frozen shoulder syndrome. The purposes of this study were to elucidate the incidence of the initial misdiagnosis with frozen shoulder syndrome among the patients with malignant shoulder tumors, and to clarify whether such initial misdiagnosis affected the time to make a final correct diagnosis or not. METHODS: Clinical records of 34 patients (age>40) with malignant shoulder tumors and those of 505 patients (age>40) with shoulder pain and stiffness were reviewed in the author's institute. The duration of the prediagnostic period was compared between the patients with and without an initial misdiagnosis as frozen shoulder syndrome. RESULTS: Among 34 tumor patients, 9 (26%) had been initially misdiagnosed with frozen shoulder syndrome. Two patients actually manifested shoulder pain and stiffness, although they did not have a record of misdiagnosis. Among 505 patients with shoulder pain and stiffness, 4 (0.8%) were diagnosed later as having malignant tumors. One of these 4 patients had been initially misdiagnosed with frozen shoulder syndrome. Consequently, 15 malignant tumors (10 bone tumors and 5 soft tissue sarcomas) were identified. Seven of them were intraosseous humeral tumors and 4 were localized in the scapular region, where patients themselves could not find them. In 10 patients, initial misdiagnosis as frozen shoulder syndrome did cause a significant delay to reach the correct diagnosis as malignant tumors (P=.035). CONCLUSION: Physicians should carefully re-examine the frozen shoulder patients with repeated plain radiographs followed by further imaging studies, if the conservative therapy fails.
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