Infiltrative Lipoma Causing Lumbar Nerve Root Compression in a Dog

Background: Lipomas are benign soft tissue mesenchymal neoplasms composed of adipose cells and are usually found in the subcutaneous tissue. Occasionally, lipomas may invade muscles or grow between them, in which case they are characterized as infiltrative lipomas. Clinical signs resulting from an intermuscular lipoma compressing peripheral nerves are rarely encountered in dogs. This case report aims to describe the neurological signs, diagnosis, and clinical evaluation of a dog diagnosed with infiltrative lipoma compressing a lumbar spinal nerve root. Case: A 12-year-old neutered male Fox Paulistinha, weighing 10.5 kg, was presented with difficulties in walking for the past 15 days with no previous history of trauma. On physical examination, the presence of three cutaneous nodules was noted in the ventral thoracic region, with onset of one year and slow and progressive growth. A cytological evaluation of the nodules was performed, and lipoma was diagnosed. At the neurological examination, the patient presented ambulatory paraparesis with marked motor deficit and atrophy of the quadriceps muscles of the left pelvic limb. Conscious proprioceptive deficit, the absence of patellar reflex, and diminished withdrawal reflex were observed in the left hind limb, in addition to diffuse pain on epaxial palpation of the lumbar region. Electroneuromyography showed increased insertion activity in the left gastrocnemius muscle and moderate spontaneous activity (fibrillation). Persistence of 10% was observed in the F-wave study of the left tibial nerve. These findings indicate partial involvement of the roots of the left sciatic-tibial nerve. Magnetic resonance imaging (MRI) showed the presence of a mass measuring 3.18 x 1.04 x 1.4 cm, interspersed with the paravertebral muscles, and located adjacent to the L2 and L3 spinous processes. An ultrasound-guided fine needle aspiration biopsy of the mass was performed and the findings of the cytopathological analysis of the collected material were considered consistent with lipoma. In view of these findings, surgical removal was recommended. However, the owner chose to attempt conservative treatment to control pain. Thus, the patient was treated with gabapentin, tramadol hydrochloride, carprofen, dipyrone, omeprazole, and physiotherapy. The animal exhibited a good response to conservative treatment, regaining its hind limb mobility in approximately 30 days. Discussion: Infiltrative lipomas compressing nerve roots are rarely described, with only one report of infiltrative lipoma in the lumbar region causing nerve root compression in dogs found in the literature. MRI was beneficial in this case, since it helped in determine the shape, location, and extent of the mass causing compression of the left L2 nerve root. The history and neurological examination findings in the patient described in this report were accounted for by the presence of an infiltrative lipoma compressing the left nerve root of L2. Surgical excision is the treatment of choice for intramuscular lipomas in most cases since conservative treatment elicits only a limited response. In contradiction to the literature, the dog in this report experienced a good response to conservative treatment, returning to normal mobility approximately 30 days after starting treatment. After six months of follow-up, the dog had not experienced a recurrence of the clinical signs. However, since the tumor has not been removed, clinical relapse is expected to occur in the future. Thus, despite the good response to conservative treatment in this case, we recommend the surgical excision of the tumor in order to decompress the affected nerve root. Although infiltrative lipomas compressing nerve roots are rare, clinicians should consider them as differential diagnosis when there is a presence of subcutaneous lipomas and neurologic signs of radiculopathy.