Neoplastic Lumbosacral Plexopathy Workup

Updated: Aug 31, 2023
  • Author: Rajesh R Yadav, MD; Chief Editor: Dean H Hommer, MD  more...
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Laboratory Studies

Results of lab studies depend on the type of cancer and the extent of involvement. Erythrocyte sedimentation rate (ESR), complete blood cell (CBC) count, alkaline phosphatase, protein electrophoresis, prostate specific antigen (PSA), and other cancer-specific labs may be abnormal, depending on the clinical situation. Uremia and hydronephrosis may be an issue with ureter obstruction, especially in patients with gynecologic malignancy.

Cerebrospinal fluid (CSF) studies may reveal elevated protein with negative cytologic findings.


Imaging Studies

The clinical diagnosis of neoplastic lumbosacral plexopathy (NLP) is confirmed by magnetic resonance imaging (MRI) or computed tomography (CT) scanning of the affected areas. MRI is preferred because it is more sensitive and provides better detail than CT scanning. [4]

MRI is more accurate in soft tissues. Hydroureter or hydronephrosis are common findings at the time of diagnosis. Diagnosis can be difficult if the scan does not show a mass lesion, but repeating the study in another 4-6 weeks often reveals pathology that was not initially apparent. Increased T2 intensity within nerve trunks, with or without enhancement, has been shown with NLP. [23]

MR neurography uses 3T MR images and improved coils to provide a clear depiction of the lumbosacral plexus and its peripheral branches. This technology can confirm a diagnosis of lumbosacral plexopathy or provide anatomic information if surgical intervention is required. [24]

CT scanning of the abdomen and pelvis is probably the most valuable in diagnosis and gives more information on bony structures. Tumor, bony erosion, and lymphadenopathy are seen in 78% of cases. Clinical findings and CT scan levels do not always demonstrate positive correlation.

Positron emission tomography (PET) scanning can aid in the detection of active malignancy in the plexus region. [25] However, the sensitivity or specificity of PET scanning in the diagnosis of tumor plexopathy is not yet clear.

Bone scanning reveals pelvic, sacral, or vertebral uptake in 60% of patients with NLP.

Myelography can be abnormal with malignant plexopathy (in 28-45% of cases).

Routine spinal and pelvic roentgenograms reveal bone destruction in 50% of patients with NLP.

In aforementioned study by Lee and colleagues, of nine patients with NLP resulting from the perineural spread of tumors from pelvic malignancies, six patients displayed abnormal signal intensity on 18F-fluorodeoxyglucose (18F-FDG) PET/CT scanning. [15]


Other Tests

See the list below:

  • Electrodiagnostic testing (electromyography [EMG], nerve conduction studies [NCSs]) reveals abnormalities in almost all patients with neoplastic lumbosacral plexopathy. [5]

    • Typical changes include acute and chronic denervation of the lumbosacral plexus. The findings are observed more extensively than would be suspected clinically. Side-to-side comparisons are helpful.

    • Myokymic discharges are not observed.

    • In the segments involved, decreased amplitudes of the evoked motor responses with normal or borderline nerve conduction velocities are noted.