The following 3 clinical phases typically characterize FS:
Phase 1 - The painful phase; the patient describes an insidious onset of predominantly nocturnal pain, usually without a precipitating factor. The pain is not related to activity, although the farthest ROM can increase the pain. As the disease progresses, patients have pain at rest. In this phase, which lasts 2-9 months, ROM is not restricted, and the diagnosis may remain unclear. [5, 6]
Phase 2 - The frozen, or adhesive, phase; the pain from phase 1 can persist, although it may decrease. Progressive limitation in ROM occurs in a capsular pattern (that is, in all directions). Normal daily activities can be severely affected. Hallmarks of this phase are an inability to move at great amplitude and an inability to move on the affected side. Diagnosis is easier in this phase than in phase 1. Although phase 2 is reported to last 3-9 months, it can persist longer than this. 
Phase 3 - The thawing, or regressive, phase; pain progressively decreases, and limitations in ROM progressively increase over 12-24 months. Although approximately 40% of patients have slight, persistent limitations in ROM, only 10% have clinically significant long-term functional limitations. 
FS can result from clinically significant trauma to the shoulder, cervical radiculopathy, pathology of the brachial plexus, any neurologic insult affecting shoulder function or innervation, or an episode of rotator cuff tendonitis. However, FS usually occurs without any clear precipitating factors. Most patients with FS have no notable history of trauma. Hence, the clinician must remember that this is an idiopathic disease in which the loss of ROM results from a dystrophic pain syndrome combined with contracture caused by an active process resembling fibromatosis.
Although patients often try to recall minor trauma associated with the onset of their shoulder symptoms, careful history taking on the part of the examiner often reveals subtle symptoms, such as night pain or pain and stiffness at the end of ROM, that predated the episode of minor trauma. In most cases, the minor trauma simply makes the patient conscious of the insidious, underlying disease process.
Patients with FS typically describe a progressive onset of pain over several weeks. Patients usually report that the initial pain was night pain or pain associated with involved movements of the shoulder (eg, combing one's hair, reaching overhead for a seat belt, reaching for one's back pocket). Combing one's hair and reaching overhead for a seat belt require a combined motion of abduction and external rotation, and reaching for one's back pocket requires extension and internal rotation of the shoulder. These combined movements tend to stretch the anterior and posterior glenohumeral capsule, respectively.
The pain of FS then progresses to a constant pain at rest that is often aggravated by any movement of the shoulder, psychological stress, exposure to cold or vibration, and changes in the weather. Patients report worsening of the pain after they engage in activities that require repetitive movements of the affected shoulder.
In about 90% of patients, the pain associated with this condition usually lasts 1-2 years before subsiding. The pain is a prominent feature of the initial phase and of the second (frozen) phase of the disease. During the thawing phase, the pain usually is less intense than it is in the other phases. It is usually felt only if the patient is moving at the end of his/her ROM (particularly in positions of subacromial impingement), if the patient performs repetitive movements of the shoulder, or if the patient is exposed to other important ergonomic stresses of the shoulder.
In the early phase of FS, the only physical finding may be pain produced at the end of ROMs in the glenohumeral joint, particularly those that stretch the capsule, such as combined abduction and external rotation (such as combing one's hair) or combined extension and internal rotation (such as reaching to scratch one's midback). During the initial, painful stage, FS may not be distinguishable from an inflammatory synovitis affecting the glenohumeral joint or from a painful episode of rotator cuff tendinopathy. In the second, or freezing, stage of the disease, contracture of the glenohumeral joint becomes readily apparent. This stage may occur only several months after the onset of symptoms.
As the condition progresses, the clinician should observe progressive limitation of the PROM, characterized by a painful capsular end-feel. The motion affected first and most severely is external rotation, followed by abduction, internal rotation, and flexion. Extension and horizontal adduction tend to be least affected. PROM of the glenohumeral joint progressively worsens over several months and may result in a loss of up to 80% of the normal movement of glenohumeral joint.
In severe cases, evaluation of AROM may show an inverted scapulothoracic motion (that is, motion of the scapula on the thorax). For example, the scapulothoracic joint initiates abduction (followed by the glenohumeral joint) to compensate for the loss of ROM in the glenohumeral joint.
On occasion, a sizable calcification of the rotator cuff in its resorptive phase may cause an acute tendinobursitis that may mimic FS. This type of acute tendinobursitis may be extremely painful, and it may result in an antalgic phenomenon, causing a loss of PROM. The acute and rapidly progressive onset of tendinobursitis over a few hours or days differentiates it from the relatively progressive onset of FS, which occurs over weeks. Another mimic of FS is severe synovitis or arthritis of the glenohumeral joint caused by an underlying primary rheumatologic inflammatory, degenerative, septic, or metastatic process.
Most patients with a painful FS have pain during resisted contraction of all of the rotator cuff tendons, during specific maneuvers designed to detect subacromial impingement (for example, the Hawkins, Neer, and Yocum maneuvers), and during maneuvers designed to detect tendinopathy of the long portion of the biceps (such as the Yergason and Speeds maneuvers). This phenomenon results because the pain generators in FS may include all of the extra-articular and intra-articular soft tissues of the glenohumeral joint and humeroscapular-motion interface (eg, subacromial bursa, rotator cuff, biceps tendon). (See Mechanics of Glenohumeral Arthritis, on the University of Washington School of Medicine Web site.)
In the presence of a clinically significant loss of PROM of the glenohumeral joint in the previously described capsular pattern, the clinician should probably be content with retaining the diagnosis of FS while de-emphasizing the aforementioned maneuvers designed to diagnose other specific, painful soft-tissue disorders affecting the shoulder.
The difficulty of accurately and reliably establishing a specific diagnosis for a painful shoulder condition based on a physician's clinical assessment should not be underestimated, as demonstrated by data from the Netherlands. The rate of interobserver agreement with regard to a diagnostic classification of shoulder disorders based on history taking and physical examination was surprisingly poor. Only moderate agreement was observed overall. The percentage of agreement was 60%, with a Cohen coefficient of 0.45 and a 95% confidence interval (CI) of 0.37-0.54. Agreement was higher than this for patients classified as having a capsular syndrome, with a Cohen coefficient of 0.63 and a 95% CI of 0.50-0.76. Disagreement was most pronounced concerning patients with severe pain, chronic complaints, and bilateral involvement.
Despite the aforementioned limitations, the diagnosis of idiopathic FS syndrome is clinically based on the patient's history and physical findings because of the poor sensitivity and/or specificity of most diagnostic tests used to confirm this condition. However, the literature offers no consensus regarding the clinical diagnostic criteria for FS. The minimal loss of ROM needed to diagnose FS varies among authors. Some suggest a loss of 2 ROMs, whereas others stipulate that the limited range must be present in all motions. [4, 5, 8, 9]
Careful neurologic examination should be conducted in all patients presenting with signs and symptoms associated with FS. Patients who have a history of smoking should undergo chest radiography with apical views to rule out a Pancoast tumor irritating the brachial plexus, which can cause FS. All patients should receive a thorough neurologic examination of the upper extremities and neck to rule out cervical radiculopathy and brachial plexopathy. Care also should be taken to look for signs of Parkinson disease, because the prevalence of shoulder pain in patients with this treatable condition is 4-5 times that of the healthy population. Furthermore, shoulder pain often is an early manifestation of Parkinson disease, and it sometimes precedes the tremor by many years. 
Proper and complete musculoskeletal and integumentary examination should be performed to rule out concomitant systemic rheumatologic, inflammatory, metastatic, or infectious disorders. Clinicians should also take the time to properly examine the thyroid gland to rule out concomitant hyperthyroidism. Physicians should remain alert to signs of unsuspected diabetes, which may be present in approximately 25% of subjects presenting with FS.
Early authors pointed to chronic inflammation as the cause of the fibrosis in FS, but objective findings have not supported this suggestion. The absence of crystals, synovial effusion, systemic symptoms, prodromal illness, and serologic markers of autoimmune or reactive arthropathic disease has limited possible theories of an inflammatory process secondary to crystalline, inflammatory, viral, or autoimmune disease.
FS remains a largely idiopathic disorder. The conditions most commonly associated with idiopathic FS are diabetes, hyperthyroidism, hypertriglyceridemia, CVA with upper-extremity paresis, brachial plexus injury, cervical spinal cord injury, and Parkinson disease. The performance of repetitive movements of the upper extremities also is associated with FS.
Anecdotal reports of patients developing FS after a coronary event or following open heart surgery are frequently found in the literature. However, the authors know of no prospective case-control study that has been conducted to confirm this supposition.
Patients who have active glenohumeral synovitis in relation to a systemic inflammatory rheumatologic disorder may develop FS as a complication of this condition. Patients who have undergone surgery to the shoulder area, with postoperative immobilization or with clinically significant pain that causes them to immobilize their shoulder, also are predisposed to develop FS.
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