Brachial and Lumbosacral Plexopathies

Published on 03/03/2015 by admin

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64 Brachial and Lumbosacral Plexopathies

Clinical Vignette

A 54-year-old man developed acute-onset right thigh, hip, and buttock pain. He also noted right knee “buckling” when he stepped off a curb, resulting in a fall. He also noted right foot drop. Paresthesias developed over the right thigh, shin, and foot. He required oral narcotics for pain relief.

His past medical history was remarkable for type II diabetes mellitus, for which he took an oral hypoglycemic. His blood sugars had been under fair control. His review of systems was remarkable for a 30-pound weight loss over the past 3 months, which he attributed to renewed efforts at dieting. He doesn’t smoke or drink heavily. He is an attorney. Family history is negative.

His general examination was unremarkable. His neurologic examination was notable for moderate weakness of right hip flexion, hip extension, knee extension, and ankle dorsiflexion. He has an absent right knee and ankle reflex, but reflexes are normal on the left lower extremity and upper extremities. Sensory testing demonstrates reduced vibration sensation at the right great toe and ankle. His gait is hesitant and reveals a right foot drop.

Electromyography (EMG) demonstrated borderline right peroneal and tibial compound motor action potentials with normal velocities and distal latencies. The sural and superficial peroneal sensory nerve action potentials were absent on the right and normal on the left. Active denervation was present in right femoral and sciatic innervated muscles, and to a lesser extent in lumbosacral paraspinals and gluteal muscles.

Magnetic resonance imaging (MRI) of the lumbosacral spine and pelvis was unremarkable, except for signal changes in denervating muscles. Lumbar puncture demonstrated an elevated cerebrospinal fluid (CSF) protein with normal cell count. Glycosylated hemoglobin was slightly elevated but otherwise his laboratory studies were normal.

He was diagnosed with diabetic lumbosacral radiculoplexus neuropathy (also known as diabetic amyotrophy). After discussion of the pros and cons he was prescribed an empiric treatment trial of intravenous methylprednisolone.

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).