Laboratory Studies
No laboratory studies help differentiate radiation-induced brachial plexopathy from other disorders involving the brachial plexus.
Imaging Studies
Plain radiography does not have diagnostic value for detecting radiation-induced brachial plexopathy.
Computed tomography (CT) scanning of the involved brachial plexus may reveal a diffuse infiltration of the tissue planes.
Magnetic resonance imaging (MRI) often reveals low signal intensity on T2-weighted images; minimal changes are found with gadolinium. [14, 20, 21]
All of these characteristics are in contrast to neoplastic processes, which would be identified by the presence of a focal mass. In addition, if traditional modalities demonstrate normal findings, positron emission tomography imaging may provide an additional tool for excluding suspected malignant plexopathy. Malignant etiologies of brachial plexopathy are associated with significantly increased uptake of 18-fluoro-2-deoxy-D-glucose, reflecting the increased metabolism associated with neoplastic processes.
Other Tests
Electrodiagnostic testing can be used to help distinguish between radiation-induced and neoplastic disorders of the brachial plexus. Generally, no significant differences between the 2 conditions are noted on sensory and motor conduction studies or late responses. However, nerve conduction studies are important to exclude other causes of paresthesias in the lateral digits, such as carpal tunnel syndrome.
Needle electromyography in radiation-induced brachial plexopathy reveals myokymia more often than in neoplastic-induced brachial plexopathy. [4] Myokymia represents spontaneous discharges accompanied by wavelike muscle quivering. The frequency may be paroxysmal motor unit action potentials or a slow continuous discharge at 1-5 Hz in motor unit action potentials. [14]
Evoked potential studies do not have any particular value for this diagnosis.
Procedures
In some cases, surgical exploration and biopsy are required to distinguish between radiation-induced and tumor-induced brachial plexopathy. Nerve grafting has been attempted in animals with fair results, but data from human trials are lacking. [22, 23]
Surgical treatment options are aimed at breaking up fibrotic tissue to eliminate mechanical constriction of the plexus and its blood supply. Attempts have been made at exoneurolysis/endoneurolysis, with or without placement of an omental or latissimus dorsi flap as a source of well-perfused tissue. Unfortunately, these approaches have proven ineffective and even harmful. Indeed, dissection alone can lead to a significant worsening of symptoms. Some relief of pain may be achieved in a minority of patients, with little or no impact on other sensory or motor deficits.
Histologic Findings
Findings may include the following:
-
Fibrosis of the neural elements and surrounding soft tissues
-
Chronic perineurial microvascular ischemia
Tables
Feature |
Tumor Infiltration |
Radiation Fibrosis |
Transient Radiation Injury |
Acute Ischemic Injury |
Incidence of pain |
80% |
18% |
40% |
Painless |
Location of pain |
Shoulder, upper arm, elbow, fourth and fifth fingers |
Shoulder, wrist, hand |
Hand, forearm |
Hand, forearm |
Nature of pain |
Dull ache in shoulder, lancinating pains in elbow and ulnar aspect of hand; occasional paresthesias and dysesthesias |
Ache in shoulder; prominent paresthesias in C-5/C-6 distribution of hand and arm |
Ache in shoulder; prominent paresthesias in C-5/C-6 distribution of hand and arm |
Paresthesias in C-5/C-6 distribution of hand and arm |
Severity |
Moderate to severe (severe in 98%) |
Usually mild to moderate (severe in 20-35%) |
Mild |
Mild |
Course |
Progressive neurologic dysfunction; atrophy and weakness in C-7/T-1 distribution, persistent pain; occasional Horner syndrome |
Progressive weakness; panplexus or upper plexus distribution; Horner syndrome uncommon |
Translate weakness with complete resolution |
Acute nonprogressive weakness and sensory loss |
Study findings |
|
|
|
|
Magnetic resonance imaging |
High signal intensity on T2-weighted images; may enhance with gadolinium |
Low signal intensity on T2-weighted images; generally nonenhancing with gadolinium |
No data |
Normal |
Computed tomography |
Mass; circumscribed or diffuse tissue infiltration |
Diffuse tissue infiltration |
Normal |
Angiography demonstrates subclavian artery segmental obstruction |
Electromyography |
Segmental slowing |
Diffuse myokymia |
Segmental slowing |
Segmental slowing |
