Introduction
For the diagnosis of the axillary neuropathy, electrodiagnostic studies are usually used to confirm axillary nerve injury and imaging tests such as ultrasonography (US) and MRI could have a complementary role for the diagnosis. We report an axillary neuropathy case after shoulder dislocation that emphasized the role of US in a unclear situation by the electrodiagnostic study.
Case Report
A 43-year-old man presented with left shoulder weakness and pain after falling down from 2-meter height vehicle following accident. The shoulder x-ray showed left shoulder dislocation and closed reduction was done. One month later, he complained of hypoesthesia in left deltoid area and left shoulder weakness. The electrodiagnostic study suggest left axillary neuropathy with partial axonotmesis state, but these were not clear for diagnosis. The compound muscle action potentials (CMAP) from bilateral deltoid muscles were similar and needle EMG of the teres minor was not done even though that of the deltoid showed denervation potentials (Table 1). US revealed hyper-echogenicity and atrophic change of left deltoid and teres minor muscles (Figure 1). The shoulder MRI was consistent with the US findings (Figure 2).
Discussion
The needle examination of teres minor is not easy due to confusion with infraspinatus and teres major. The interpretation of axillary neuropathy with normal nerve conduction study is not easy without needle abnormal finding of teres minor muscle. US of the axillary nerve was described by Martinoli et al at 2004, in that the adjacent posterior circumflex artery could aids the identification of the nerve. However, it is a challenging task due to its small size and deep course. US of the teres minor is easy to localize because it is just below the infraspinatus and just under the skin or the posterior deltoid. Teres minor arise from middle third of lateral border of the scapula and insert at the inferior posterior greater tubercle of the humerus. When evaluating teres minor, placing transducer over the posterior part of shoulder joint and guiding it below the scapular spine on sagittal plane, then the teres minor and infraspinatus may be seen. A small bony ridge is the landmark for separating these two muscles and the smaller and round shape one is the teres minor. Teres minor atrophy can be assessed by comparing with the appearance of infraspinatus on sagittal scans. It should be further studied that US finding of the axillary nerve in the axillary neuropathy and the easier method of approaching the axillary nerve.
Conclusion
The US of the deltoid and teres minor muscle and axillary nerve could be complementary role for the diagnosis when the result of electrodiagnostic studies are obscure. |
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The electrodiagnostic study suggest left axillary neuropathy with partial axonotmesis state.
a,b. Shoulder US demonstrates hyper-echogenicity of left deltoid muscle (a: left, b: right). c,d. Shoulder US demonstrates hyper-echogenicity and atrophy of left teres minor muscle (c: left, d: right). Del, Deltoid; Tm, Teres minor; InfraS, Infraspinatus
T2-weighted TSE sagittal MRI at the level of teres minor shows the high signal intensity with the decreased volume of the muscle. Arrow, Teres minor
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