Infraspinatus muscle palsy involving suprascapular nerve, brachial plexus or cervical roots related to inflammatory or mechanical causes: Experience of 114 cases.

OBJECTIVES: To report a large series of neurogenic infraspinatus muscle (ISM) palsy, in order to improve knowledge of diagnosis, diverse etiologies and care management.

METHODS: Clinical and electrodiagnostic (EDX) data for 114 cases of ISM palsy were collected over a 21-year period. Cases were attributed to 4 clinical conditions: (1) isolated suprascapular nerve mononeuropathy (n=48), (2) multiple mononeuropathies (n=33), (3) plexus lesions (n=17), and (4) cervical radiculopathy (n=16). These were related to 2 mechanisms: inflammatory (dysimmune) and mechanical.

RESULTS: Group 1 cases were younger, had the most severe ISM palsies, were mostly related to inflammatory lesions (81%) such as neuralgic amyotrophy (NA), and frequently had delayed diagnosis because disability was mild. Group 2 cases were all related to inflammatory lesions and had slightly less severe ISM palsies that were frequently hidden by winged scapula. In groups 3 and 4, ISM palsies were milder and all cases were related to mechanical lesions such as brachial plexus trauma or C4-C5-C6 radiculopathy. In these cases, deltoid and ISM palsies were equal in frequency and severity whereas biceps brachii impairment was less frequent and much milder. Deltoid palsy frequently appeared predominant as compared with ISM palsy, because upper limb elevation palsy was more disabling than external rotation palsy.

CONCLUSIONS: ISM palsy is a rare condition, often under-diagnosed and misidentified. The 4 main conditions of ISM palsy may be recognized by careful clinical, EDX and other examinations when necessary. Analysis of the present series highlights some clinical and EDX points that should help non-specialist and even specialist clinicians who are faced with this rare condition, to distinguish mechanical and inflammatory causes, and thus adapt patient management accordingly.