Plexopatía lumbosacra metastásica por adenocarcinoma microscópico de origen primario desconocido. Reporte de un caso

Metastatic lumbosacral plexopathy secondary to microscopic adenocarcinoma of unknown primary origin: A case report

Introducción. La plexopatía lumbosacra metastásica es una complicación poco frecuente causada principalmente por tumores colorrectales y ginecológicos, sarcomas y linfomas. Se caracteriza por dolor en la parte baja de la espalda, las nalgas, los muslos o las caderas.

Presentación del caso. Mujer de 33 años, quien en noviembre del 2021 consultó al servicio de neurocirugía de un hospital de cuarto nivel de atención de Cuenca, Ecuador, por dolor urente y lancinante en las regiones lumbosacra e inguinal durante los últimos 10 meses. En el examen físico se evidenció pérdida de la función motora en flexores y extensores de ambas caderas con debilidad e hipoestesia en el costado izquierdo y afectación del miembro inferior derecho. En febrero de 2022 una tomografía computarizada de columna dorsolumbar mostró disminución del espacio intervertebral L5-S1, pinzamiento en L5 con nódulo de Schmörl y lesión lítica en L5. En abril, a partir del análisis inicial de la biopsia de la lesión, se diagnosticó plasmocitosis reactiva, pero en mayo, por persistencia de la sintomatología, la muestra fue enviada a una segunda revisión que concluyó adenocarcinoma tubular metastásico. En julio una resonancia magnética contrastada confirmó deposito tumoral metastásico en L5 con compromiso de la raíz nerviosa y afectación del sacro, por lo que se diagnosticó plexopatía lumbosacra metastásica por adenocarcinoma microscópico de tumor primario desconocido. Se realizó cirugía estabilizadora de columna lumbosacra y se inició tratamiento de radioterapia, lográndose una disminución considerable del dolor.

Conclusión. La plexopatía lumbosacra metastásica es una afección poco frecuente que debe sospecharse en pacientes con dolor intenso en la parte baja de la espalda y en las extremidades inferiores. Su diagnóstico puede retrasarse debido a resultados iniciales inespecíficos o no concluyentes en estudios histopatológicos, por lo que es importante reevaluar las muestras con resultados negativos para malignidad.

Introduction: Metastatic lumbosacral plexopathy is a rare complication mainly caused by colorectal and gynecological tumors, sarcomas, and lymphomas. It is characterized by pain in the lower back, buttocks, thighs, or hips.

Case Presentation: In November 2021, a 33-year-old woman presented to the neurosurgery department of a tertiary care hospital in Cuenca, Ecuador, due to a 10-month history of burning and lancinating pain in the lumbosacral and inguinal regions. Physical examination revealed loss of motor function in both hip flexors and extensors, along with weakness and hypoesthesia on the left side and involvement of the right lower limb. In February 2022, a computed tomography (CT) scan of the thoracolumbar spine showed reduced L5-S1 intervertebral space, L5 compression with a Schmorl’s node, and a lytic lesion at L5. In April, based on the initial analysis of the biopsy of the lesion, reactive plasmacytosis was diagnosed, but in May, due to persistent symptomatology, the sample was sent for a second review, which concluded metastatic tubular adenocarcinoma. In July, contrast-enhanced magnetic resonance imaging (MRI) confirmed a metastatic tumor deposit at L5 with nerve root involvement and sacral infiltration. A diagnosis of metastatic lumbosacral plexopathy caused by microscopic adenocarcinoma of unknown primary origin was established. Lumbosacral stabilization surgery was performed, followed by radiotherapy, which resulted in significant pain relief.

Conclusion: Metastatic lumbosacral plexopathy is a rare condition that should be suspected in patients presenting with severe lower back and lower limb pain. Its diagnosis may be delayed due to nonspecific or inconclusive initial histopathological findings. Therefore, it is essential to re-evaluate samples with negative results for malignancy.

https://doi.org/10.15446/cr.v11.117705

Keywords: Lumbosacral Plexus; Peripheral Nervous System Diseases;
Adenocarcinoma; Neoplasm Metastasis; Neoplasms, Unknown Primary

Palabras clave: Plexo lumbosacro; Neuropatías Periféricas; Adenocarcinoma; Neoplasias Metastásicas; Neoplasias de Origen Primario Desconocido

Alan Omar Sarmiento-Tapia

Instituto Ecuatoriano de Seguridad Social (IESS) -
Hospital de Especialidades José Carrasco Arteaga -
Neurosurgery Service - Cuenca - Ecuador

Milton Mauricio Sanmartin-Plaza

Pablo Andrés Dután-Patiño

Universidad de Cuenca - Faculty of Medical Sciences -
Department of Internal Medicine -
Cuenca - Ecuador

Mauricio Alejandro Ovando-Aquino

Hospital General Vicente Corral Moscoso -
Anatomic Pathology Service -
Cuenca - Ecuador

Corresponding author

Milton Mauricio Sanmartin-Plaza.
Departamento de Medicina Interna, Facultad de Ciencias Médicas, Universidad de Cuenca. Cuenca. Ecuador.
Correo electrónico: mauricio.sanmartinp@ucuenca.edu.ec

Received: 14/01/2025 Accepted: 23/11/2025

Abstract

Resumen

IntroducTIOn

Lumbosacral plexopathy is a neurological disorder caused by injury or dysfunction of the lumbosacral plexus nerves, a nerve network formed by the anterior rami of spinal roots L1 to S4 (1). Patients with lumbosacral plexopathy typically present with lower back and lower limb pain, motor weakness, numbness, paresthesia, and sphincter dysfunction; however, physical findings vary depending on the severity and location of involvement and can range from foot drop to specific patterns of muscle weakness and sensory loss (1,2). Given that the lumbosacral plexus is located close to the abdominal and pelvic organs, lumbosacral plexopathy can have multiple etiologies (1,3), with diabetes mellitus, traumatic injury, neoplasms, penetrating trauma, and pregnancy being the most common (1).

Metastatic lumbosacral plexopathy is a rare complication (4–7) characterized by involvement of one or more nerves of the lumbosacral plexus secondary to malignant tumor infiltration.(7) It occurs most frequently in association with colorectal and gynecologic malignancies, as well as sarcomas and lymphomas(4,8), and typically presents with a subacute onset of pain in the lower back, buttocks, thighs, or hips, depending on the region of the lumbosacral plexus involved. Although data on its incidence and prevalence are limited, metastatic lumbosacral plexopathy has been reported to occur in 0.71% of patients with cancer(7). In addition, it may be found as the initial manifestation of cancer in approximately 15% of cases(7).

Treatment of lumbosacral plexopathy is directed toward the specific underlying cause and symptom relief (1,2). In cases of metastatic lumbosacral plexopathy, management depends on the primary neoplasm (2), requires an interprofessional approach (7), and is palliative. Therapeutic options include surgical tumor resection in selected cases, radiotherapy to the plexus, systemic chemotherapy, interventional pain management procedures, and symptomatic treatment (4,7,8).

The following is the case of a patient with metastatic lumbosacral plexopathy from an unknown primary tumor, who underwent surgery and radiotherapy, with a satisfactory clinical outcome.

Case presentation

In November 2021, a 33-year-old mixed-race woman, biochemist by profession, attended an outpatient consultation with the neurosurgery service of a tertiary care health institution in Cuenca, Ecuador, due to burning and lancinating pain (10/10 on the Visual Analog Scale [VAS]) starting in the lumbosacral region and extending to the inguinal region. The pain, which appeared 10 months earlier on the right side and progressively became bilateral, radiated in a radicular pattern to the right lower limb (extending to the distal region of the foot) and left lower limb (posterior middle third of the thigh). It caused her difficulty to fall and stay asleep and worsened with walking, lifting weight, and prolonged sitting. One month after the onset of pain, the patient developed difficulty with defecation and urination.

The patient reported a term pregnancy with a normal delivery and the use of oral contraceptives as her current family planning method. Her family history included the death of her mother due to amyotrophic lateral sclerosis and of her maternal grandmother due to pharyngeal cancer.

On physical examination during the consultation, it was found that the patient had loss of motor function in the hip flexors and extensors bilaterally, along with weakness and hypoesthesia in the left hip, as well as involvement of the right lower limb characterized by hyporeflexia, foot drop, and hypoesthesia extending from the posterior and medial aspects of the leg to the foot. In addition, impaired joint proprioception in the joints and absence of the Achilles reflex were observed in the right foot.

During the neurological examination, tactile, pain, and vibratory sensations were assessed using absorbent cotton, a pin, and a 128 Hz tuning fork, respectively. Examination revealed bilateral hypoesthesia to tactile and pain stimuli in the L4-L5 dermatomes, suggesting sensory involvement at that level. On the left side, the patient perceived the stimulus on the proximal thigh but reported reduced or absent sensation over the medial aspect of the leg (L4) and on the dorsum of the foot (L5). Vibratory sensation was preserved above these areas, establishing a symmetrical sensory level at L4-L5. There were no signs of upper motor neuron involvement or sphincter dysfunction.

On February 25, 2022, at the request of the neurosurgery service, the patient underwent an outpatient computed tomography (CT) scan of the thoracolumbar spine, showing narrowing of the L5-S1 intervertebral disc space, L5 nerve root impingement associated with a Schmörl’s node, and a lytic lesion at L5. Considering these findings, the patient was admitted for further evaluation, including a bone marrow biopsy and a computed tomography-guided biopsy of the L5 vertebral body lesion.

The first procedure was performed in March 2022, and the results showed no anatomical changes suggestive of neoplastic involvement. The second procedure was performed in April 2022, and the results showed a presumptive diagnosis of reactive plasmacytosis. Moreover, after completion of the lesion biopsy, an intraoperative follow-up CT scan revealed vertebral body collapse caused by an approximately 80% space-occupying lesion, with a high risk of fracture.

On May 24, due to clinical deterioration (prostration and wheelchair dependence for mobility) and high suspicion of malignancy, the lesion biopsy sample was submitted for a second histopathological review. This analysis concluded that the findings were consistent with metastatic tubular adenocarcinoma, with an immunohistochemical profile (positive for CKAE1-AE3 and CK7, and negative for CK20, CD56 and CD138), suggesting a possible breast, endometrial, or ovarian origin (Figures 1, 2, and 3).

Figure 1. Immunohistochemical analysis of the lesion biopsy. Cytokeratin 7 (CK7) immunostaining shows strong and diffuse cytoplasmic expression in the cytoplasm of the tumor cells, supporting an epithelial origin.

Source: Image taken while conducting the study.

Figure 2. Immunohistochemical analysis of the lesion biopsy at high magnification (40×). Cohesive epithelioid cells arranged in incomplete glandular structures with poorly defined lumina are observed. The cells exhibit abundant amphophilic cytoplasm, oval nuclei with dense chromatin, and mild anisonucleosis.

Source: Image taken while conducting the study.

Figure 3. Immunohistochemical analysis of the lesion biopsy at low magnification. A proteinaceous background with diffuse lymphocytic infiltrate is observed. A bone spicule and a small cluster of cohesive neoplastic cells are identified at the periphery of the specimen.

Source: Image taken while conducting the study.

In May 2022, while the patient remained hospitalized under the care of the neurosurgery service, a tumor marker test was performed, as well as ferritin, iron, lactate dehydrogenase (LDH), total calcium, and phosphorus blood tests, all of which were within normal values. In June 2022, a positron emission tomography-computed tomography (PET/CT) scan was performed, revealing a lytic lesion at the L5 vertebral body without evidence of a metabolically active primary tumor. Finally, in July 2022, a contrast-enhanced MRI of the lumbosacral plexus was performed, which demonstrated a metastatic tumor deposit at L5 (primary tumor undetermined), with nerve root involvement and probable neoplastic infiltration with metastasis affecting the sacrum, together with a diffuse disc protrusion with posterocentral extrusion at the L5-S1 level (Figure 4).

Figure 4. Contrast-enhanced magnetic resonance imaging of the lumbosacral plexus. T1-weighted images show contrast enhancement of the bilateral lumbosacral plexus nerve roots, with associated sacral involvement.

Source: Image taken while conducting the study.

Given the findings, on July 5, 2022, the patient was diagnosed with metastatic lumbosacral plexopathy due to microscopic adenocarcinoma of unknown primary tumor. The case was presented to the oncology department, which, after joint evaluation with the neurosurgery service, planned lumbosacral spine stabilization surgery followed by initiation of targeted radiotherapy to the lumbosacral plexus.

The patient underwent surgery on August 2, 2022, and was discharged 8 days later with instructions to continue outpatient management with gabapentin (600 mg orally every 8 hours), paracetamol (1 000 mg, orally every 6 hours), and oral morphine (5 mg orally every 4 hours), which she continued until January 2023. On August 26, 2022, she initiated palliative radiotherapy, receiving a total dose of 24 Gy delivered in 12 fractions, administered Monday through Friday.

Six follow-up visits were conducted at 4-week intervals, during which a progressive reduction in pain was observed, reaching a VAS score of 3/10 at the last visit in January 2023. The patient was subsequently lost to follow-up, as she did not attend further appointments, and at the time of writing this case report, no additional information regarding her clinical status was available.

Discussion

Lumbosacral plexopathy is a neurological disorder resulting from injury to or dysfunction of the nerves of the lumbosacral plexus and may arise from multiple etiologies (1), as summarized in Table 1:

Table 1. Causes of lumbosacral plexopathy.

Category	Specific causes
Tumor or mass	Malignant invasion: colon, cervix, ovary, bladder, prostate Metastases: breast, lung, lymphoma
Infection	Local organs: gastrointestinal tract, urinary tract, and spinal cord Generalized: human immunodeficiency virus (HIV)
Trauma	Traffic accident Sports injury Postoperative period
Radiation
Hematoma
Vascular lesions
Inflammatory / microvasculitis	Diabetic lumbosacral radiculoplexus neuropathy Lumbosacral radiculoplexus neuropathy Post-surgical inflammatory neuropathy Sarcoidosis

Source: Elaborated based on Dyck et al. (2)

Neoplasms are the most common non-traumatic cause of lumbosacral plexopathy (2). In this regard, it has been established that it may result from direct invasion by a primary tumor, metastatic disease, or as a complication of radiotherapy (9). In the present case, lumbosacral plexopathy was caused by an unknown primary tumor that metastasized to the spine (L5).

From a clinical perspective, neoplastic lumbosacral plexopathy typically presents with a subacute onset of pain localized to the lower back, buttocks, thighs, or hips (2,3), depending on the specific segment of the lumbosacral plexus involved (2), as observed in our patient, who presented with pain in the lumbosacral region radiating to the lower limbs. It is noteworthy that, although pain associated with neoplastic lumbosacral plexopathy is characteristically aggravated when lying down and relieved by standing and walking (2), our patient reported worsening of pain when walking. This finding may be explained by structural mechanical compression (due to vertebral and sacral infiltration), neurogenic claudication (secondary to L4-L5 radicular involvement), or nerve ischemia (possibly related to tumor infiltration of the vasa nervorum).

Lumbosacral plexus involvement usually occurs after the diagnosis of malignancy. In this regard, Altinişik-İnan et al. (6) reported that, as of 2022, only one case had been described in the literature in which lumbosacral plexopathy preceded the diagnosis of a pelvic malignancy. Therefore, the relevance of the present case lies in the low prevalence of reported cases in which, despite extensive diagnostic evaluation, the primary tumor could not be identified. Furthermore, it is noteworthy that, despite an initial diagnosis of plasmacytoma, clinical suspicion persisted and, owing to the perseverance of the medical team, the case was successfully reoriented through a second histopathological review.

Metastatic lumbosacral plexopathy is usually diagnosed after an analysis of clinical, neuroimaging, and electrophysiological features (8), with MRI and CT being the most commonly used imaging tests to confirm the diagnosis (5,8), as in the present case.

The treatment of metastatic lumbosacral plexopathy depends on the underlying malignancy (2), is mainly supportive, and focuses on effective pain management and the prevention of mobility complications secondary to neuromuscular dysfunction. It includes surgical tumor resection in selected cases, radiotherapy directed to the plexus, systemic chemotherapy, interventional pain management procedures, and symptomatic treatment (8). In the present case, palliative treatment was chosen with the main objective of controlling pain, taking into account the poor prognosis reported in the literature for patients with this condition.

Conclusions

Metastatic lumbosacral plexopathy is a rare condition that should be suspected in patients presenting with severe lower back and lower limb pain. Diagnosis may be delayed due to initial non-specific or inconclusive histopathological findings; therefore, in the presence of high clinical suspicion or progressive symptoms, re-evaluation of specimens initially negative for malignancy is essential. Timely diagnosis and treatment are crucial to prevent irreversible physical and neurological deterioration, optimize clinical outcomes, and improve the efficacy of therapeutic interventions, thus contributing to a comprehensive approach to these neoplasms.

Ethical considerations

For the preparation of this case report, the patient provided written informed consent authorizing the use and publication of her clinical data. Confidentiality was maintained throughout the manuscript.

Conflicts of interest

None stated by the authors.

Funding

None stated by the authors.

Acknowledgments

To the patient, for her support and for authorizing the publication of her case.

References

1.Dydyk AM, Hu Y, Hameed S. Lumbosacral Plexopathy. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 [cited 2025 Dec 3]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK556030/.

2.Dyck PJB, Thaisetthawatkul P. Lumbosacral plexopathy. Continuum (Minneap Minn). 2014;20(5):1343-58. https://doi.org/ghz8xm.

3.Brejt N, Berry J, Nisbet A, Bloomfield D, Burkill G. Pelvic radiculopathies, lumbosacral plexopathies, and neuropathies in oncologic disease: a multidisciplinary approach to a diagnostic challenge. Cancer Imaging. 2013;13(4):591-601. https://doi.org/qg4v.

4.Jaeckle KA. Nerve plexus metastases. Neurol Clin. 1991;9(4):857-66. https://doi.org/qg4w.

5.Kang MS, Kim N, Kim KH, Kim DH. Neoplastic lumbosacral plexopathy in untreated cervical cancer: A case report. J Electrodiagn Neuromuscul Dis. 2022;24(2):42-5. https://doi.org/qg4x.

6.Altinişik-İnan G, Aral İP, Yaşar-Daşgin F, Ercan K, Aytaç-Arslan S. Plexopathy due to bilateral lumbosacral plexus involvement in a patient with prostate cancer: A case report and review of the literature. Turk J Med Res. 2022;30(3):192-5. https://doi.org/qg4z.

7.Harish-Bindiganavile S, Prabhu A. Neoplastic Lumbosacral Plexopathy. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 [cited 2025 Dec 3]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK564296/.

8.Jaeckle KA. Neurologic manifestations of neoplastic and radiation-induced plexopathies. Semin Neurol. 2010;30(03):254-62. https://doi.org/db4vgm.

9.Güzey FK, Güzey D, Çelik AS, Aycan A, Kaplan R, Özkan N. Lumbosacral plexopathy in a patient with metastasis of cervix carcinoma: A case report. Turkish Neurosurgery. 2006;16(4):204-7.