A 52-year-old woman presents to her primary care physician with a 5-month history of progressive right shoulder pain and stiffness. She reports that the pain initially began as a dull ache in the lateral deltoid region but has since evolved into a constant stiffness that interferes with her ability to dress herself and reach for items in her kitchen cabinets. She has a 10-year history of type 2 diabetes mellitus, which is currently managed with metformin and glipizide. On physical examination, there is no evidence of muscle atrophy or localized swelling. Active abduction of the right shoulder is limited to 80° and external rotation is limited to 20°. Passive range of motion is identically restricted in the same planes. Strength testing of the rotator cuff muscles is 5/5 within the patient's limited range of motion. Radiographs of the right shoulder show no joint space narrowing, osteophytes, or fractures.
Which of the following is the most likely diagnosis?
The correct answer is:
A) Adhesive capsulitis
The patient’s presentation is classic for adhesive capsulitis, or "frozen shoulder," which is characterized by the insidious onset of shoulder pain followed by a progressive, global loss of both active and passive range of motion. The hallmark that distinguishes adhesive capsulitis from other shoulder pathologies on the USMLE is this concordant loss of active and passive motion, typically most pronounced in external rotation. The condition is caused by fibroblastic proliferation and contraction of the glenohumeral joint capsule. This patient has diabetes mellitus, which is the most significant risk factor for developing adhesive capsulitis and is associated with a more severe and protracted clinical course.
Answer choice B: Bicipital tendonitis, is incorrect. Bicipital tendonitis typically presents with localized pain over the anterior shoulder in the bicipital groove. While it can cause pain with movement, it does not result in a global restriction of passive range of motion.
Answer choice C: Glenohumeral osteoarthritis, is incorrect. While osteoarthritis also causes a loss of both active and passive range of motion, it typically presents in older patients with a much more gradual onset. Furthermore, radiographs in osteoarthritis would characteristically show joint space narrowing, subchondral sclerosis, and osteophytes, which were noted to be absent in this patient.
Answer choice D: Polymyalgia rheumatica, is incorrect. This inflammatory condition causes pain and stiffness in the shoulder and hip girdles, but the stiffness is typically bilateral and systemic. While patients may have difficulty moving due to pain, they do not have the mechanical, capsular restriction of passive range of motion seen in adhesive capsulitis.
Answer choice E: Rotator cuff tear, is incorrect. A full-thickness rotator cuff tear classically presents with a loss of active range of motion and objective weakness (e.g., a positive drop-arm sign). However, in a rotator cuff tear, the passive range of motion remains relatively preserved because the joint capsule itself is not fibrosed.
Key Learning Point
Adhesive capsulitis is a clinical diagnosis characterized by a global, progressive loss of both active and passive range of motion, particularly in external rotation. It is strongly associated with diabetes mellitus and thyroid disorders. Unlike rotator cuff tears, passive motion is limited; unlike osteoarthritis, radiographs are typically normal.
