Neuralgic amyotrophy (acute brachial plexitis) is a disorder of acute nerve injury often triggered by an acute infectious illness, immunization, or surgery. It has many potential presentations but usually affects nerve trunks of the shoulder girdle, upper trunk nerve fibers, and parts of peripheral nerve trunks of the arm. Winging of the scapula from long thoracic neuropathy, inability to externally rotate the shoulder from suprascapular neuropathy, and inability to abduct the shoulder from axillary neuropathy are common presentations. Spontaneous improvement occurs in most individuals over 6 to 12 months.
Progressive brachial plexus lesions may result from infiltrative processes, such as malignancy, that spread from local structures, such as the lung (Pancoast tumor) and breast. These tumors tend to involve the lower trunk/medial cord first, producing sensory loss in the fourth and fifth fingers and weakness of intrinsic muscles of the hand. A progressive brachial plexopathy can also result from radiation therapy close to the brachial plexus performed years earlier for treatment of these malignancies.
A slowly progressive lower trunk brachial plexopathy (neurogenic thoracic outlet syndrome) can arise from a fibrous band extending from an elongated C7 transverse process to the first thoracic rib. This anatomic anomaly causes compression of the T1 anterior primary ramus before it merges with the C8 segment to form the lower trunk, producing a classic clinical presentation of numbness of the medial hand and forearm, along with weakness and atrophy of thumb and other intrinsic hand muscles. Progression of weakness is halted by surgical section of the offending fibrous band.
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