What are the causes, clinical features, and epidemiology of lumbosacral plexopathy?

Lumbosacral Plexopathy: Causes, Clinical Features, and Epidemiology

Lumbosacral plexopathy encompasses a diverse range of etiologies including entrapment neuropathies, inflammatory/immune-mediated processes, neoplasms, and idiopathic causes, presenting with pain, weakness, and sensory deficits across multiple peripheral nerve distributions in the lower extremities. 1

Causes

Entrapment Neuropathies

• Entrapment neuropathies are common causes of lumbosacral plexopathy resulting from spinal or extraspinal compression 1
• Piriformis syndrome is a frequently described cause of extraspinal nerve entrapment, where the sciatic nerve is compressed by the piriformis muscle due to anatomic variation or an associated fibrous band 1
• Lateral disc herniations compressing the distal nerve root lateral to the neural foramen may cause plexopathy that is not detected on standard lumbar spine MRI 1

Neoplastic Causes

• Primary tumors of the lumbosacral plexus are most commonly benign peripheral nerve sheath tumors (schwannomas and neurofibromas) 1
• Malignant peripheral nerve sheath tumors are rare and occur more frequently in patients with neurofibromatosis 1
• Other primary malignant or metastatic tumors can involve the lumbosacral plexus, with plexopathy sometimes being the first clinical presentation of neoplastic disease 1
• Non-neoplastic masses that can involve the plexus include hematoma, abscess, aneurysm, amyloidosis, and endometriosis 1

Inflammatory/Immune-Mediated Causes

• Diabetic amyotrophy (Bruns-Garland syndrome) is a well-recognized cause of lumbosacral plexopathy 2, 3
• Acute inflammatory demyelinating polyneuropathy (Guillain-Barré syndrome) can present with lumbosacral plexopathy 1
• Chronic inflammatory demyelinating polyneuropathy (CIDP) may affect the lumbosacral plexus 1
• Idiopathic lumbosacral plexopathy is considered the lower limb equivalent of neuralgic amyotrophy (Parsonage-Turner syndrome) 2

Other Causes

• Ischemic nerve injury can lead to lumbosacral plexopathy 1
• Hereditary neuropathies (e.g., Charcot-Marie-Tooth disease) may present with plexopathy 1
• Sarcoidosis can involve the lumbosacral plexus 1
• Infectious causes (e.g., zoster-associated limb paresis) can affect the plexus 1

Clinical Features

Pain Characteristics

• Intense pain in one or both legs is a hallmark feature 2
• Pain distribution crosses multiple dermatomes, distinguishing it from radiculopathy 4
• Pain is typically acute or subacute in onset 5

Motor Symptoms

• Asymmetrical multifocal weakness follows the pain, typically within weeks or months 2, 5
• Weakness occurs in regions innervated by multiple nerves from the affected plexus 4
• Muscle atrophy develops in the affected areas 5

Sensory Symptoms

• Sensory loss occurs across multiple nerve distributions 6
• Paresthesias, hypesthesia, and allodynia are common sensory manifestations 5

Autonomic Dysfunction

• Autonomic symptoms may be present in some cases 5

Diagnostic Approach

Clinical Diagnosis

• The clinical and electrodiagnostic features of lumbosacral plexopathy and radiculopathy often overlap 1
• Diagnosis requires clinical suspicion combined with thorough anatomical knowledge and meticulous examination 3

Imaging

• MRI of the lumbosacral plexus is the imaging modality of choice due to superior soft-tissue contrast and spatial resolution 7, 8
• MR neurography at 3.0T provides excellent depiction of the lumbosacral plexus and its peripheral branches 7, 8
• CT with IV contrast can be useful when MRI is contraindicated, offering the next highest level of anatomic visualization 1

Electrodiagnostic Studies

• Electrodiagnostic examination shows important acute motor and sensory axonal loss, characterized by denervation and low-amplitude sensory action potential 2
• These studies help confirm abnormalities in multiple nerve distributions 4

Course and Prognosis

• Idiopathic lumbosacral plexopathy generally runs a monophasic and self-limiting course 5
• Recovery is slow, taking 6 to 36 months 2
• Recovery is often incomplete 2, 5

Treatment Considerations

• Treatment generally combines analgesics with narcotic agents, neuropathic pain medication, short-term corticosteroids, and rehabilitation 2
• In severe cases, long-term corticosteroids and other immunosuppressive agents may be required 2
• Currently, there is no evidence from randomized trials to support any recommendation on the use of any immunotherapy treatment in idiopathic lumbosacral plexopathy 5

Common Pitfalls in Diagnosis

• Failure to distinguish between plexopathies and radiculopathies, which typically follow a single dermatome distribution 4
• Overlooking lumbosacral plexopathy as a diagnosis until all other radicular, plexal, and truncal origins have been ruled out 2
• Not recognizing that lateral disc herniations may cause plexopathy that is not detected on standard lumbar spine MRI 1