64 Brachial and Lumbosacral Plexopathies
The most important diagnostic tool for the evaluation of a possible plexopathy is a thorough and accurate history. The history-taking must be aided by a solid understanding of the risk factors for development of brachial or lumbosacral plexopathy. The most common etiologies of plexopathy are trauma, surgery (e.g., related to arm or leg positioning, injury with regional anesthetic block), birth injury, inherited genetic mutations (e.g., hereditary neuralgic amyotrophy), a primary autoimmune process (e.g., Parsonage–Turner, also known as neuralgic amyotrophy), previous radiotherapy, and neoplastic invasion (Fig. 64-1; Table 64-1). Systemic vasculitis and peripheral nerve sarcoidosis are other uncommon etiologies. Diabetes mellitus is a risk factor for an immune-mediated lumbosacral (and less often, brachial) plexopathy, that is, diabetic lumbosacral radiculoplexus neuropathy (diabetic LRPN) secondary to microvasculitis. Thus, if a prior or concomitant history of any of these risk factors (e.g., previous surgery, trauma, or family history, diabetes) is present, the clinician should strongly consider that etiology yet not necessarily forget to consider other plausible etiologies. It is also helpful to remember that recent infection, vaccination, and parturition are triggers for the immune-mediated plexopathies, especially brachial plexopathies (e.g., hereditary neuralgic amyotrophy and neuralgic amyotrophy). There are often other clues about etiology found in the symptomatology of the plexopathy. For example, the abrupt, spontaneous onset of shoulder and upper extremity symptoms favors an immune-mediated (e.g., microvasculitic) mechanism, such as that seen with hereditary neuralgic amyotrophy, neuralgic amyotrophy and diabetic cervical radiculoplexus neuropathy (diabetic CRPN), whereas a more gradual or insidious onset of symptoms would point toward neoplastic invasion or postradiotherapy plexopathy. Immune-mediated plexopathies (e.g., diabetic LRPN or neuralgic amyotrophy) usually begin with severe pain, lasting days to weeks, followed by the development of weakness a few days to a few weeks later. Radiation-associated plexopathy (e.g., for breast cancer) usually presents with much less pain than plexopathy due to malignancy or due to immune-mediated mechanism. Radiation-induced brachial or lumbosacral plexopathy usually presents more gradually and can occur months to decades after radiotherapy. Recurrent, painful brachial plexopathy is most typical of hereditary neuralgic amyotrophy. The recognition of accompanying symptoms is also important. For example, weight loss is a common accompaniment of diabetic LRPN or diabetic CRPN, as well as plexopathies secondary to neoplasm or a more systemic process such as vasculitis.
Table 64-1 Brachial Plexus Etiologies
| Mechanism | Examples | Comments |
|---|---|---|
| Trauma, traction | Motorcycle injury, cardiothoracic surgery | Often severe degree, poor prognosis |
| Stinger | Football etc. | Good prognosis |
| Perinatal | Mixed mechanisms | Generally good prognosis |
| Idiopathic | Autoimmune? | Self-limited |
| Hereditary | Genetically determined | Recurrent, benign |
| Malignancy | Infiltration of tumor cells | Poor prognosis |
| Radiation | RoRx-induced ischemia | Prognosis guarded but not suggestive of recurrent tumor |
| Knapsack, rucksack, etc | Compression | Usually self-limited |
| Thoracic outlet | Entrapment | Rare, confused with CTS |
| Heroin induced | Indeterminate |
CTS, carpal tunnel syndrome; RoRx, radiation therapy.
In the case presented above, the temporal evolution was of an abrupt-onset neuropathic process that caused motor and sensory dysfunction. The neuropathic process involved one lower extremity. The pain was so severe that the patient required narcotics. The patient had not experienced antecedent trauma, surgery, or radiotherapy. There was no family history of plexopathy. These factors suggested that an immune-mediated plexopathy was likely. Furthermore, the clinical setting was remarkable for diabetes mellitus and significant weight loss, and as diabetes mellitus is believed to be a risk factor for immune-mediated plexopathy and many of these patients experience contemporaneous weight loss, this diagnosis was most likely. Thus, the most likely etiology in this patient was DLRPN. Additional evaluation, including examination, electrodiagnostic testing and imaging, further supported the diagnosis (Fig. 64-2).
