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Brachial and Lumbosacral Plexopathies
Clinical Vignette
A 54-year-old man developed acute-onset right thigh, hip, and buttock pain. He reported 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 did not smoke or drink heavily. He was an attorney. Family history was 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 had an absent right knee and ankle reflex, but reflexes were normal on the left lower extremity and upper extremities. Sensory testing demonstrated reduced vibration sensation at the right great toe and ankle. His gait was hesitant and revealed 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. A lumbar puncture demonstrated an elevated cerebrospinal fluid (CSF) protein with a 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 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 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), injury at birth, inherited genetic mutations (e.g., hereditary neuralgic amyotrophy), primary autoimmune processes (e.g., Parsonage–Turner, also known as neuralgic amyotrophy), previous radiotherapy, and neoplastic invasion ( Fig. 59.1 ; Table 59.1 ). 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, known as diabetic lumbosacral radiculoplexus neuropathy (DLRPN). Thus, if a prior or concomitant history of any of these risk factors (e.g., previous surgery, trauma, diabetes, or family history of plexopathy) is present, the clinician must take that into consideration. It is also helpful to remember that recent infection, vaccination, and parturition are triggers for the immune-mediated plexopathies, especially brachial plexopathies. There are often other clues about etiology found in the presenting symptoms. For example, the abrupt, spontaneous onset of shoulder and upper extremity symptoms favors an immune-mediated mechanism, such as that seen with hereditary neuralgic amyotrophy, neuralgic amyotrophy, and diabetic cervical radiculoplexus neuropathy (diabetic CRPN). A more gradual or insidious onset of symptoms would point toward neoplastic invasion or postradiotherapy plexopathy. Immune-mediated plexopathies (e.g., DLRPN, CRPN, or neuralgic amyotrophy) usually begin with severe pain, lasting days to weeks, followed by the development of weakness a few days to weeks later. Radiation-associated plexopathy usually presents with less pain and has a more gradual onset, often 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 DLRPN or CRPN, as well as plexopathies secondary to neoplasm or a systemic vasculitis.
Causes of Brachial Plexopathy.
TABLE 59.1
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 earlier, the temporal evolution was of an abrupt-onset neuropathic process in 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 weight loss. Diabetes mellitus is believed to be a significant risk factor for immune-mediated plexopathy. Many of these patients experience contemporaneous weight loss. Additional evaluation, including examination, electrodiagnostic testing, and imaging, further supported the diagnosis of DLRPN ( Fig. 59.2 ).
Parsonage-Turner Brachial Plexitis.
Clinical Presentation
Plexus lesions commonly result in unilateral or asymmetric extremity muscle weakness and sensory complaints that do not conform to the distributions of single roots or nerves. Brachial plexopathies cause shoulder girdle weakness if the upper plexus is involved and hand weakness if the lower or medial plexus is principally involved. Sensory loss is usually variable but follows a similar pattern; for example, a medial plexus lesion causes numbness of the fourth and fifth fingers. Autonomic disturbances, caused by disruption of the sympathetic fibers traversing the lower trunk to the superior cervical ganglia of the brachial plexus, may be present and include trophic skin changes, edema, reflex sympathetic dystrophy (complex regional pain syndrome), and Horner syndrome (miosis, ptosis, ipsilateral facial anhidrosis).
Upper plexus lesions of the lumbar plexus cause weakness of thigh flexion, adduction, and knee extension. Lower sacral plexus lesions result in weakness of thigh extension, knee flexion, foot dorsiflexion, and plantar flexion. Sensory changes are seen in both lesions. Complete lumbosacral plexopathy produces weakness and muscle atrophy throughout the lower extremity, with total areflexia and anesthesia. Concurrent autonomic loss results in warm, dry skin and peripheral edema.
In addition to differentiating etiologies for plexopathy, the clinician needs to consider mimickers. The presence of neuropathic pain can reasonably exclude pure motor processes, such as motor neuronopathies (e.g., amyotrophic lateral sclerosis), disorders of neuromuscular junction transmission (e.g., myasthenia gravis), and myopathies. Orthopedic injuries can sometimes mimic plexopathy; electrodiagnostic testing may rule out underlying nerve damage. The most important mimic of plexopathy is polyradiculopathy; nerve root lesions also present with both weakness and pain. The mechanism of nerve root injury may be structural (e.g., neural foraminal stenosis or disk herniation), infectious (e.g., Lyme neuroborreliosis), or neoplastic (e.g., carcinomatous meningitis).
Anatomy
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