The causes of a difficulty in shoulder elevation are often difficult to identify because this complaint might originate from shoulder and cervical spine root disorders. In addition, the age at occurrence of cervical spine and shoulder pathologies is very similar, particularly among the aging population [1,2]. Therefore, cervical spine and shoulder pathologies are often misdiagnosed. Among these conditions, cervical spondylotic amyotrophy (CSA) and rotator cuff tears are often confused because the main symptom in both is difficulty in shoulder elevation.

CSA is classified into proximal and distal types [3,4,5]. The clinical characteristics of the proximal type of CSA are muscle atrophy in the upper extremities, no or insignificant sensory deficit and lower extremity symptoms, and weakness of the deltoid and biceps, which often causes drop shoulder [3,4,5,6,7]. Patients with CSA are frequently referred to orthopedic surgeons specializing in shoulder surgery.

Usually, conservative therapy is effective for CSA, but surgery is occasionally needed if conservative therapy is ineffective. The duration of symptoms is a risk factor for poor outcome after surgical treatment [8,9]; hence, early diagnosis is very important. The aim of the present study was to identify physical findings useful for differentiating between CSA and rotator cuff tears to prevent the misdiagnosis of CSA as a rotator cuff tear.

In the present study, 10 patients (40.0%) with CSA were misdiagnosed as having rotator cuff tears on initial diagnosis. Therefore, we surmise that CSA is highly likely to be misdiagnosed as a rotator cuff tear. Some prior reports discuss the differential diagnosis between cervical and shoulder pathologies with respect to the causes of localized shoulder pain [1,2]. However, to the best of our knowledge, there are no reports on the differential diagnosis between cervical and shoulder pathologies with respect to the causes of difficulty in shoulder elevation.

CSA is classified into two types based on its clinical features. Proximal-type CSA presents with atrophy and weakness of the deltoid and biceps and originates from the C5 or C6 roots or anterior horns [3,4,5,6,7]. Distal-type CSA presents with atrophy and the weakness of extensor and flexor muscles of the fingers and intrinsic hand muscles and originates from the C7–T1 roots or anterior horns [3,4,5,6,7]. The major symptom of proximal-type CSA is difficulty in shoulder elevation caused by weakness of the deltoid and biceps. In addition, the age at which cervical spine and shoulder pathologies occur is very similar, particularly among the aging population [1,2]. Therefore, proximal-type CSA is often misdiagnosed as a shoulder disorder, particularly as a rotator cuff tear. Conservative therapy is usually effective in CSA; however, if it is ineffective, surgery is needed [8,9]. Tauchi et al. [8] reported that early surgery was recommended for CSA patients in whom conservative treatment was unsuccessful based on the clinical status before surgery, including symptom duration. Uchida et al. [9] reported that a long preoperative period was strongly correlated with low muscle power improvement. Early diagnosis is therefore vital.

The diagnosis of CSA is comprehensively based on physical findings, disease course, findings of imaging modalities such as MRI and CT myelography, and electromyographic findings [11,13,14,15]. However, imaging studies and electromyography generally cause a delay in the diagnosis and entail a high cost, whereas physical findings are convenient to assess and enable rapid diagnosis [1]. Therefore, we identified the physical findings useful for differentiating between CSA and rotator cuff tears to prevent the misdiagnosis of CSA as a rotator cuff tear, particularly on initial diagnosis.

We chose five physical findings specific to CSA and observed them in both CSA and rotator cuff tear patients. Nishijima et al. [10] reported that to fully extend the shoulders, similar to a swallow tail, the posterior fibers of the deltoid are essential. They named this physical finding the swallow-tail sign; this finding enables the evaluation of the posterior fibers of the deltoid [10]. Each finding involved in disorders of the C5 or C6 nerve roots or anterior horn was specific to CSA. We calculated the sensitivity and specificity of each physical finding.

Physical findings related to the deltoid, such as weakness and atrophy of deltoid and the swallow-tail sign, were highly sensitive but not highly specific. Therefore, these physical findings might be positive, to some extent, in patients with rotator cuff tears. Kido et al. [16] reported that the average decrease in the muscle volume of shoulders with rotator cuff tears is 19%–30% in the rotator cuff muscles and 29% in the deltoid muscle. Therefore, deltoid function might be affected by a rotator cuff tear.

The physical findings related to the biceps, such as weakness and atrophy of the biceps, were both highly sensitive and specific. Therefore, these physical findings could be useful for differentiating between CSA and rotator cuff tears.

Our study has several limitations. First, we did not evaluate the coexistence of CSA and a rotator cuff tear, i.e., patients with CSA, except those misdiagnosed with rotator cuff tears on initial diagnosis, did not undergo examinations for rotator cuff tears, and patients with rotator cuff tears did not undergo examinations for CSA. Second, we did not evaluate inter- and intra-observer errors. However, the evaluation of muscle weakness was based on MMT, which is generally accepted worldwide as a reliable test for assessing muscle strength [12]. Evaluations of muscle atrophy and the swallow-tail sign were based on laterality; therefore, inter- and intra-observer errors might have been fewer. Third, we did not conduct a power analysis to determine the appropriate sample size before conducting the present study; the number of cases is also comparatively few. However, because there was a significant difference in each physical finding, we must consider the possibility that a type 2 error (caused by a small sample size) might not have occurred.

We believe that physical findings related to the biceps muscle play a vital role in the initial differential diagnosis between CSA and rotator cuff tears. Imaging methods such as MRI, CT myelography, and electromyography are needed for a more accurate diagnosis. We suggest that in patients with suspected disorders of shoulder elevation, physicians should perform a physical examination to evaluate the biceps, including tests for weakness and atrophy. Thus, we can prevent the misdiagnosis of CSA as a rotator cuff tear and a delay in diagnosing CSA. If these physical findings are positive, more accurate diagnostic tools such as MRI, CT, and electromyography can be used.

CSA is highly likely to be misdiagnosed as a rotator cuff tear. Weakness and atrophy of the biceps are useful findings to differentiate between CSA and rotator cuff tears and prevent misdiagnosis.