OBJECTIVES: The objective of this study was to estimate the prevalence of undiagnosed diabetes mellitus in patients with newly diagnosed frozen shoulder (FS) and study whether diabetes mellitus increases the severity of FS disease.

METHODS: Patients with newly diagnosed FS were consecutively included in this case-control study. Patients who were not already diagnosed as having diabetes mellitus were invited to be tested with the hemoglobin A1c blood sample test. The study population was compared with a control group, consisting of five individuals from the general population matched on age and sex. The passive range of motion, Oxford Shoulder Score, and visual analog scale (VAS) for average and maximum daily pain was recorded for all of the patients in the study group.

RESULTS: A total of 235 patients were included, 34 (14%) of whom were diagnosed as having diabetes mellitus before the examination. Of the remaining 201 patients, 122 (61%) agreed to be tested for diabetes mellitus. None of the tested patients had undiagnosed diabetes mellitus. This was not significantly different from the prevalence in the matched control population (P = 0.09). There was no difference between patients with and without diabetes mellitus in average daily VAS (P = 0.46) nor maximum daily VAS (P = 0.44). The Oxford Shoulder Score was similar in the two groups (P = 0.23) as was the range of motion.

CONCLUSIONS: The prevalence of undiagnosed diabetes mellitus is low in patients with FS and does not differ from the general population. Diabetes mellitus does not seem to affect patients' perceived severity of an FS.