Lumbosacral Plexopathy

Lumbosacral plexopathy is dysfunction of the lumbar (L1 to L4) and sacral (L4 to S4) plexuses, causing leg weakness and sensory loss in several nerve distributions. Causes are diabetes (radiculoplexus neuropathy), retroperitoneal haematoma, abscess, tumour (colorectal, gynaecological, prostate, lymphoma, sarcoma), radiation injury, pelvic surgery, obstetric injury, aneurysm, trauma and inflammatory or ischaemic neuropathy.

Pathophysiology. Direct infiltration, compression, ischaemia, radiation fibrosis or inflammatory microvasculitis injures the plexus.

Pain in the back, pelvis or leg, then weakness, wasting and sensory loss in the thigh and leg, depending on the plexus level (lumbar: quadriceps, hip flexion and adduction; sacral: foot drop, hamstrings, glutei). Tumour causes progressive pain, leg swelling or rectal symptoms. Radiation plexopathy is painless, with weakness appearing months to years after treatment.

Red flags.

• Acute leg weakness with anticoagulation (retroperitoneal haematoma).
• Progressive painful weakness with weight loss or known cancer.
• Fever or back pain (abscess).

Electromyography and nerve conduction studies localise the lesion and exclude radiculopathy or mononeuropathy. MRI of lumbosacral plexus and pelvis (with contrast), CT or PET-CT for tumour and haematoma. Check glucose, HbA1c, inflammatory markers, coagulation and cancer markers. Biopsy for suspicion of tumour. In radiation plexopathy, myokymic discharges on electromyography help.

Differential diagnosis.

• Lumbosacral radiculopathy, cauda equina syndrome and conus lesions.
• Femoral, sciatic and other mononeuropathies.
• Diabetic radiculoplexus neuropathy, Guillain-Barre syndrome and motor neuron disease.

Treat the cause.

• Haematoma: stop and reverse anticoagulation, with surgery for compressive haematoma.
• Abscess: antibiotics and drainage.
• Tumour: oncology, radiotherapy, chemotherapy or surgery.
• Diabetic or inflammatory: glycaemic control, with consideration of immunotherapy.

Pain. Gabapentin 300 mg three times daily, increased to 600 to 1200 mg three times daily, pregabalin, duloxetine 60 mg daily or amitriptyline 10 to 75 mg at night. Opioids for cancer pain. Nerve blocks and neuromodulation in refractory cases.

Radiation plexopathy. No proven treatment: pain control, physiotherapy, anticoagulation or hyperbaric oxygen have been tried with uncertain benefit.

Rehabilitation. Physiotherapy, orthoses, walking aids and falls prevention.

Monitoring. Strength, pain and imaging as required.

Referral and escalation. Refer to neurology, oncology and surgery as needed.