Pathologic data are sparse, but Suarez and coworkers (1996) have reported collections of intense mononuclear inflammation in fascicles of the plexus obtained by biopsy. Perivascular lymphocytes were found in the endoneurial space and, less so, in the epineurium.
Therapy is purely symptomatic, but we have usually embarked on a course of steroids and, in a few cases, other immunosuppressants, when the illness continued to advance over many weeks. Corticosteroids sometimes have a beneficial effect on pain and have also been successful in some cases of lumbosacral plexitis. Uncontrolled observations by van Eijk and coworkers on the use of prednisolone in 50 patients have suggested that pain relief and motor outcome were better than in untreated patients.
Heredofamilial Brachial Plexopathy (Hereditary Neuralgic Amyotrophy, SEPN1 Mutation)
Rarely, an acute and painful recurrent brachial neuropathy occurs in a familial pattern. The inheritance is autosomal dominant and the attacks, occur most commonly in the second and third decades of life. The authors have observed this syndrome in 3 generations of a family, some members having had 5 attacks at ages ranging from 3 to 45 years. We have had experience with the contemporaneous onset of brachial plexitis in an adult brother and sister who shared the same household but had no family history of a similar problem. A shared exposure to viral or environmental agents was suspected. Lower cranial nerve involvement and mononeuropathies in other limbs are conjoined in some instances (see Taylor). Attacks may be spontaneous or precipitated by compression, slight stretching, or minor trauma to the region of the plexus. In one family, attacks have been triggered by events that activate the immune system (fevers, infections, surgical procedures). In several such families, there are subtle characteristic facial features including narrowed and horizontally positioned eyes and a long nasal bridge (Modigliani face). Cleft palate and unusual skin folds and creases have been observed in other kindreds (Jeannet et al).
The typical course is usually benign with good recovery of each episode, but residual deficits may accumulate after recurrent attacks. In Dutch families affected by the disease, Alfen and colleagues have pointed out that some patients experience a more chronic and undulating course rather than discrete attacks.
Madrid and Bradley examined the sural nerves from two patients with familial recurrent brachial neuropathy. In teased single nerve fibers they found sausage-like segments of thickened myelin and redundant loops of myelin with secondary constriction of the axon. In addition, nerve fibers showed a considerable degree of segmental demyelination and remyelination. They called this aberration of myelin formation “tomaculous” neuropathy (from tomaculum, “sausage”), changes that are now appreciated as valid but relatively nonspecific.
The genetic basis for this is a mutation of SEPN1. Another cause of recurrent brachial palsy, or of derivative syndromes involving nerves in the arms, is HNPP, discussed in the earlier section on inherited neuropathies and due to a deletion in the PMP22 gene (“Hereditary Neuropathy With Pressure Palsies”). As commented there, the gene defect is also on chromosome 17, but it is not the one associated with familial brachial neuritis (see Chance et al). Some confusion has arisen because CMT1A, HNPP, and the familial brachial palsy disease all have chromosome 17 defects. Pressure palsies in HNPP are painless and there is usually an underlying and slowly advancing polyneuropathy. In some families, such as the one reported by Thomas and Ormerod, the distinction between hereditary neuralgic amyotrophy (HNA) and HNPP was unclear as the recurrent brachial plexopathies were painful (consistent with the former), but there was also a painless multifocal sensory neuropathy (consistent with the latter).