La complexité anatomique du plexus brachial rend difficile l’exploration électrophysiologique de ses atteintes. Cette exploration est pourtant nécessaire pour guider la thérapeutique, notamment dans la perspective d’une reconstruction chirurgicale post-traumatique. L’évaluation vise à localiser aussi précisément que possible le site des lésions au sein du plexus, ainsi qu’à apprécier leur sévérité et leur pronostic de récupération. Elle repose sur la détermination de la topographie des signes cliniques, complétée par l’étude des potentiels sensitifs et l’enregistrement EMG des muscles « marqueurs ». Étant donné la complexité anatomique du plexus brachial, nous proposons d’en conduire l’exploration selon des règles de simplification tirées de l’analyse des schémas anatomiques. L’étude des schémas incite à isoler deux règles d’exploration : d’une part, individualiser les atteintes des différents troncs plexiques en tableaux sémiologiques distincts, comme on le fait pour les nerfs périphériques et pour les racines ; d’autre part ramener les tableaux d’atteinte des troncs primaires aux tableaux connus d’atteinte des racines cervicales, tandis que les tableaux d’atteinte des troncs secondaires seront ramenés aux tableaux connus d’atteinte des troncs nerveux du membre supérieur. La méthode de simplification proposée permet à la fois de démystifier les atteintes plexiques et d’en faciliter la compréhension et l’exploration.

The anatomic complexity of the brachial plexus makes its electrophysiological exploration difficult. Electrodiagnosis nevertheless plays a crucial role in assessing brachial plexopathies, particularly in the perspective of post-traumatic surgical reconstructions. The evaluation aims to locate as precisely as possible injuries within the plexus, as well as to determine their severity and capacity for recovery. This requires various sensory nerve conduction studies and needle EMG recordings of “marker” muscles. Plexopathies differ from radiculopathies by altered sensory nerve responses and unaltered functional innervation of paracervical muscles. We propose to simplify the exploration of brachial plexopathies by following some practical rules derived from a reanalysis of the brachial plexus anatomic sketch. Two main simplification rules can be deduced from an analysis of the anatomic sketch. First it would be judicious to associate the plexopathies involving a single element of the brachial plexus with distinct etiological and symptomatic patterns according to the altered element, as one does for peripheral nerve and root pathologies. The second proposal relies on the observation that each supraclavicular “truncal” element (upper, middle, or lower) of the brachial plexus results from reunion of cervical root nerves and behaves like a “super-root” for the upper limb, while each infraclavicular “cord” element (posterior, lateral, or medial) is the sum of two or more peripheral nerves and behaves like a “super-nerve”. Accordingly, the motor and sensory abnormalities associated with the lesion of a single plexus branch may occupy a clinical and electrophysiological territory that recovers those of its constituants. Except the unaltered paracervical muscles, it is useful to reduce the topographical semiology of truncal lesions to well-known cervical radiculopathies (upper trunk neuropathy to C5 and C6 associated radiculopathies, middle trunk neuropathy to C7 radiculopathy, lower trunk neuropathy to C8 and T1 associated radiculopathies); and that of cord lesions to well-known mononeuropathies of the upper limb (for example, a posterior cord neuropathy may be considered as a full radial mononeuropathy associated with an axillary one). This method of simplification allows to demystify the brachial plexopathies and to facilitate their comprehension and exploration.