When Shoulder Weakness Points to the Nerve

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Shoulder weakness is often linked to rotator cuff injury or structured pathology, but nerve-related causes should also be considered.

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This case highlights suprascapular neuritis presenting with marked weakness and muscle wasting following a brief episode of severe shoulder pain, with MRI playing an important role in identifying muscle denervation and excluding mechanical compression.

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Case

‍Severe pain followed by persistent weakness

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A 45-year old male patient presented with a six-month history of left shoulder weakness. At the time of his visit, he did not have any significant shoulder pain (or other symptoms).

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Talking with him however he did report experiencing a ten-day period, immediately prior to developing his current symptoms, where he had experienced severe pain in his shoulder.

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Clinical Examination

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On examination there was visible wasting within the infraspinous fossa and significant weakness of external rotation.

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There was mild weakness of resisted supraspinatus testing (empty can) but no clear wasting. His shoulder examination was otherwise normal.

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There was a normal spin examination and no other focal neurological signs.

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Findings

MRI evidence of muscle denervation

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An X-ray of the shoulder was normal.

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MR images demonstrate atrophy and marked oedema within the supraspinatus and infraspinatus muscle bellies. There is no fatty replacement.

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The remainder of the rotator cuff musculature, deltoid and the partially visualised trapezius are normal in signal.

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Perineural fat planes are maintained around the suprascapular nerve within the infraspinatus fossa, spinoglenoid notch and suprascapular notch. The nerve appears anatomically normal.

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There is no evidence of mechanical compression.

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Discussion

‍A characteristic presentation of brachial neuritis

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This patient was diagnosed with brachial neuritis (Parsonage-Turner syndrome)

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The sudden onset of short-lived, sever shoulder pain followed by weakness is a characteristic history for this problem.

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The absence of clear trauma, history of repeated overhead activity or a structural lesion on MR imaging also make this diagnosis more likely.

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He has been referred for nerve conduction studies / EMG to help confirm the distribution of nerves affected, and to provide an indication about nerve reinnervation and prognosis.

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He has been advised that spontaneous recovery is the most likely outcome however this may take up to 36 months.

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The role of MRI and nerve conduction studies

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Muscle denervation has multiple possible causes, including trauma, neuropathies, infection and neoplasia.

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MRI is a very useful study as it can both diagnose muscle denervation and help determine why this has occurred (for example by illustrating a structural lesion).

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MRI demonstrates characteristic signal intensity patterns depending on the chronicity of muscle denervation.

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In the acute or sub-acute phases, as illustrated by this case, denervation muscle shows a high signal intensity pattern on fluid sensitive sequences and normal signal intensity on T1-weighted MRI images.

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In chronic denervation, muscle atrophy and fatty infiltration can be seen. This is generally best seen on T1-weighted sequences with high signal and volume loss.

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Nerve conductions studies and EMG are often done alongside MR imaging.

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These tests can help localise areas of compression or neuropathy and can provide information and functional recovery.