Neoplastic lumbosacral plexopathy (NLP) is an infrequent complication associated with advanced systemic cancer due to local or regional progression of the primary tumor. NLP is characterized by significant pain and sensorimotor deficits.
Anatomically, the lumbosacral plexus consists of lumbar (L1-L4) and sacral (L5-S5) portions, which are connected by the lumbosacral trunk (L4-L5).The L1-L4 nerve roots transverse through psoas muscle and then coalesce into the lumbar plexus, which then divides into anterior and posterior divisions. The first 3 nerves (iliohypogastric, ilioinguinal, femoral) of the 7 major branches of lumbar plexus provide motor and sensory innervation to the abdominal wall. The next 3 nerves (lateral femoral cutaneous, femoral, obturator) innervate the anteromedial thigh. The femoral nerve terminates into the saphenous nerve, providing sensation along the medial aspect of the leg.
The sacral plexus also divides into anterior and posterior divisions, which further divide into various peripheral nerves that provide sensory motor innervation to the posterior hip girdle, thigh, and anterior and posterior leg. The 5 main nerves are the superior gluteal, inferior gluteal, posterior femoral cutaneous, sciatic, and pudendal nerves. The sciatic nerve divides into the common peroneal and tibial nerves in the thigh.
NLP associated with pelvic, abdominal, and retroperitoneal tumors often results in significant pain, sensory disturbance, weakness, and disability.  Plexus involvement occurs as a result of tumor extension or invasion and heralds a progressive disease course. Plexopathy is part of the initial presentation of cancer in 15% of patients.
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Lumbosacral plexus involvement occurs most commonly due to intra-abdominal tumor extension (73% of cases); it occurs less commonly with growth from metastases, lymph nodes, or bone structures. A tumor can invade the plexus directly or track along the connective tissue or epineurium of nerve trunks.
The most prevalent types of tumors are colorectal tumors (20%), sarcomas (16%), breast tumors (11%), lymphoma (9%), and cervical tumors (9%).  Other tumors, including multiple myeloma, account for another 37% of cases. The most common distant metastatic lesions are caused by breast cancer. In one study, the lumbosacral plexus was involved in 50 of 2261 cases of cervical cancer; however, it was involved in 38 of the 74 patients (51%) in the subgroup with proven retroperitoneal metastatic disease.
The lower (sacral) plexus is involved most frequently (approximately 50%), followed by upper plexus involvement (more than 30%) and panplexopathy (18%).  Bilateral plexopathy occurs in 25% of cases and is usually caused by breast cancer metastases. Lower plexus involvement occurs generally with colorectal and cervical neoplasms. Involvement of the sacral sympathetic nerves is less common (10%).
Malignant psoas syndrome (MPS) was first described in 1990 by Stevens and refers to severe and difficult pain due to proximal lumbosacral plexopathy, painful fixed flexion of the ipsilateral hip, and radiologic or pathologic evidence of malignant involvement of the ipsilateral psoas major muscle. 
The incidence of neoplastic lumbosacral plexopathy is 0.71%.
Significant morbidity from neoplastic lumbosacral plexopathy occurs due to associated pain, weakness, and sensory deficits.  One study noted median survival of 5.5 months after diagnosis. In patients with prostate cancer,  symptoms may persist for years and survival may be longer.
No known correlation is recognized between the incidence of neoplastic lumbosacral plexopathy and race.
One study noted a male-to-female ratio for neoplastic lumbosacral plexopathy of 1.3:1, although the investigation involved just a small number of patients.
In one study, age at the time of presentation of neoplastic lumbosacral plexopathy ranged from 19-80 years, with a median age of 65.5 years.
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