Shoulder Calcific Tendinitis Presenting as Septic Arthritis: A Case Report.

Calcific tendinitis of the shoulder is a common condition in which calcium hydroxyapatite crystals form within the rotator cuff tendons, most often the supraspinatus. As a sequela of this condition, long-term discomfort may develop with intermittent acute flares. Symptoms can also arise suddenly, causing intense pain and limited shoulder motion. These effects are often reflected in patient-reported outcome measures, for example, overall limitations in upper-extremity function and overhead activity. During flares, symptoms can mimic septic arthritis. This occurs on clinical exams and imaging. Accurate diagnosis is therefore difficult. Misdiagnosis may lead to unnecessary procedures or inappropriate treatment. Careful assessment with ultrasound and MRI helps distinguish calcific tendinopathy from infection. Recognizing typical features and choosing the right imaging are essential for optimal care. A 42-year-old man with a year of right-shoulder pain had a sudden flare with fever and chills, raising concern for septic arthritis. Despite normal inflammatory markers, empiric IV antibiotics were started; MRI then showed supraspinatus calcific deposits and subacromial-subdeltoid bursitis without effusion or infection. Antibiotics were stopped, and the diagnosis was revised to acute calcific tendinitis. He underwent arthroscopic debridement with tendon repair, followed by physiotherapy, with marked symptomatic and functional improvement. Acute calcific tendinopathy (ACT) of the shoulder often mimics septic arthritis. Abrupt pain, restricted motion, and occasional marker elevation, sometimes fever with crystal rupture, can prompt misdiagnosis and unwarranted antibiotics or surgery. Diagnosis rests on exam plus imaging: radiographs/ultrasound show calcifications and MRI helps exclude infection. In our case, early imaging and multidisciplinary review prevented unnecessary antimicrobials and enabled timely arthroscopy.