By Michael Rubin, MD

Professor of Clinical Neurology, Weill Cornell Medical College

Dr. Rubin reports he is a consultant for Merck Sharp & Dohme Corp.

SYNOPSIS: Brachial plexopathy associated with cancer may involve any region of the brachial plexus and can be distinguished from radiation-induced brachial plexopathy only by the use of high-resolution magnetic resonance imaging.

SOURCE: McNeish BL, Zheutlin AR, Richardson JK, Smith SR. Primary cancer location predicts predominant level of brachial plexopathy. Muscle Nerve 2020; June 8. doi:10.1002/mus.26994. [Online ahead of print].

Shoulder and axillary pain are the most common presenting symptoms of neoplastic-induced brachial plexopathy (NIBP). Involvement of the inferior trunk is more common than that of the upper trunk, and breast and lung cancer are the most frequent neoplasms. Distinguishing cancer recurrence from radiation-induced brachial plexopathy (RIBP) can be challenging. Horner syndrome, pain at symptom onset, and lower plexus involvement traditionally are more likely in NIBP, whereas RIBP often is painless early on, is associated with more severe paresthesiae and weakness than NIBP, and tends to affect the upper trunk. In the era of computer-guided radiation dosing, targeting, and delivery, is this traditional approach to causation and localization still correct?

In this retrospective electronic medical record review, researchers analyzed all nerve conduction (NCS) and needle electromyography (EMG) studies performed at The Michigan Medicine Electrodiagnostic Laboratory in Ann Arbor from January 2008 through January 2019 and coded for brachial plexopathy. Collated information included age, gender, cancer type, clinical symptoms, radiation history, imaging information, and NCS/EMG findings. Inclusionary criteria required presenting symptoms consistent with brachial plexopathy in a patient with a history of cancer and radiation therapy. Patients with a history suggesting trauma or neuralgic amyotrophy (Parsonage-Turner syndrome) were excluded. NCS required the presence of decreased motor and sensory amplitudes, with abnormal spontaneous activity and high-amplitude, long-duration motor-unit potentials and reduced recruitment on needle EMG study. Spontaneous activity included positive sharp waves, fibrillation potentials, and myokymic discharges. Imaging results indicating the presence or absence of tumor invasion of the plexus and/or adjacent lymph nodes differentiated NIBP from RIBP, respectively. Statistical analysis comprised Student’s t-test, chi-square test, logistic regression, and bivariate analyses, with 0.05 used as the threshold for statistical significance.

Among 912 cases of brachial plexopathy, 22 were diagnosed as NIBP and 34 as RIBP. NIBP more often presented with pain, but there was no difference between NIBP and RIBP in the distribution of predominant trunk involved. The primary cancer location (superior or inferior to the clavicle) was significantly associated with plexopathy location (upper or lower trunk) in both NIBP (P = 0.047) and RIBP (P = 0.003), and multivariate analysis revealed that the primary cancer location superior or inferior to the clavicle was the strongest predictor of upper or lower trunk involvement, respectively. Infraclavicular tumors (e.g., lung and breast cancers) were highly predictive of predominantly lower trunk plexopathy, whereas supraclavicular tumors (e.g., head and neck cancers) were predictive of upper trunk plexopathy, regardless of whether the injury was related to radiation or neoplastic invasion. As the authors concluded, current high-resolution imaging contradicts the traditional teaching around localization of brachial plexus lesions.

COMMENTARY

Other studies report different findings. Among 44 patients with breast cancer seen at the Asian Medical Center in Seoul, South Korea, between 2000 and 2016, of whom 41 were evaluated by EMG, upper trunk involvement of the brachial plexus was most frequent, affecting 22%. Lower trunk involvement was seen in 9.9%. Among 19 patients who underwent magnetic resonance imaging, supraclavicular-region metastases were found in 57.9%. It would appear that metastases from either above or below the clavicle may affect either the upper or lower portions of the brachial plexus. Clinical observation and imaging indicate that any cancer can affect any part of the brachial plexus.¹

REFERENCE

1. Kim J, Jeon JY, Choi YJ, et al. Characteristics of metastatic brachial plexopathy in patients with breast cancer. Support Care Cancer 2020;28:1913-1918.