Differential Diagnosis in Neurology

9.3. Tumors of the Lumbosacral Plexus

• General Features:
  • Occurs in less than 1% of patients with neoplasm
  • Direct extension in approximately 75%; metastasis from extra abdominal sites in approximately 25%
  • In approximately 15% of patients lumbosacral plexopathy is the initial presentation
  • The lumbar plexus is affected in approximately 1/3 of patients; the sacral plexus in 50% and the rest in both plexuses (L5); bilateral involvement is seen in 25% of patients
  • Tumors that involve the lumbosacral plexus
    • Colorectal, prostate, uterus, ovary are the primary tumors
    • Invade by local extension
    • Most common cause of lumbosacral plexus lesions is from is a colorectal tumor
  • Metastatic lesions:
    • Breast
    • Lymphoma
    • Sarcoma
    • Lung
    • Thyroid
    • Melanoma
    • Testicular
• Clinical presentations:
  • Severe unilateral pain radiating into L1–L4 roots; costovertebral angle pain
  • Weakness of proximal roots L1–L4 with psoas and quadriceps weakness
  • Lower extremity edema
  • Warm dry foot if sympathetics are involved
  • Lymphoma and lymphosarcoma may attain large size and present as a mass in the abdomen
  • CT scan and MRI positive > 80% of the time by the time of clinical presentation
  • Sacral bone involvement is often a sign of colorectal cancer
  • Poor prognosis (less than two years)
• Primary pelvic plexus tumors:
  • Neurofibroma (nerve sheath tumor)
  • Schwannoma
  • Sarcoma (degeneration of benign neurofibroma)
• Benign tumors:
  • Compress the lumbosacral plexus
  • Dermoid of the omentum
  • Uterine leiomyoma

Irradiation Therapy

• X-RT may induce:
  • Malignant nerve sheath tumor
  • Post irradiation lower motor neuron syndrome
• X-RT therapy:
  • General features:
    • Usual cancers irradiated are:
      • Lymphoma
      • Testicular
      • Ovarian
      • Uterine
      • Cervical
    • Median time to onset of symptom is variable; usual is 5 years; some patients symptoms appear 30 years later
    • No relation between amount of X-RT and the latent period to symptoms
    • Rarely occurs with less than 4000 rads
    • Presents 1–5 years after external or internal cavity irradiation
• Clinical Presentation:
  • Bilateral slowly progressive leg weakness
  • Starts distally; usually L5–S1 roots; wasting and absent reflexes
  • Numbness and paresthesias may be presenting symptoms
  • Mild pain is late a symptom (approximately 50% of patients); aching, burning and lancinating in character
  • May arrest after several years (usually 5 years)
  • Associated bowel and bladder symptomatology from X-RT
  • CSF protein may be increased
  • Radiation osteitis of the sacrum (rare)
  • EMG:
    • Myokymia in 60% of patients

Radiation vs Tumor Invasion of the Lumbosacral Plexus

• Radiation Plexopathy
  • Insidious onset and progression
  • First symptom is weakness
  • Bilateral involvement
  • Distal muscle weakness (L5–S1 roots)
  • Negative CT/MRI
  • EMG: Myokymia and fasciculation
• Tumor Invasion
  • Rapid onset and progressive
  • Pain is in the initial symptom
  • Unilateral involvement
  • Proximal weakness (L1–L4 roots)
  • Enhancing mass on MRI: destruction of bone
  • No Myokymia

Post-Irradiation Lower Motor Syndrome

• X-RT of the lower thoracic and lumbar spine
• Painless wasting and fasciculation of leg muscles
• May have delayed onset from end of X-RT (months to years)
• EMG:
  • Denervation in the affected muscles
  • Sensory nerve action potentials and somatosensory evoked potentials are normal
• Sphincter function is normal