The cause of BPN is unknown. The clinical course and a possible association with viral infection, immunization, and especially interferon therapy suggest an inflammatory-immune mechanism. Evidence implicates both humoral and cellular immune mechanisms. Antibodies to peripheral nerve myelin may be present. Clinically there are similarities between BPN and the brachial neuropathy of serum sickness, further suggesting BPN may be an immune-modulated disease.
The pathology is not well studied. Mononuclear cell infiltrates have been reported. In a series of brachial plexus dissections the presence of prominent collections of inflammatory cells(esp. T lymphocytes) in the brachial plexus were noted. The lesions were marked by focal lymphocytic inflammatory infiltrates, with a lymphoid germinal center and onion-bulb formation.
G.A. Suarez, et.al. Immune Brachial Plexus Neuropathy. Neurology, Feb. 1996, p.559-562
Submitter's Note (Lon Morgan, DC) - This paper suggests to that patients with brachial neuritis not obviously of NMS origin should be evaluated for possible immune system involvement.