Aspectos clínico-patológicos da neoplasia da bainha de mielina no plexo braquial com infiltração do canal medular em um cão

Background: Primary neoplasms of peripheral nerves are uncommon in domestic animals and are mainly represented by nerve sheath tumors. They occur especially in the peripheral nerves of the brachial plexus, and may occasionally invade and compress the spinal cord. Initial clinical diagnosis is challenging, since the main clinical sign is a progressive claudication, whose origin, neurogenic or musculoskeletal, is not usually defined. The objective of this report is to describe clinical, ultrasonographic, tomographic and histopathological findings in a peripheral nerve sheath tumor in the brachial plexus of a dog, to assist clinicians making an early diagnosis, so patients can attain longer survival. Case: A 9-year-old, male, intact, Dachshund was presented to a veterinary neurologist with a history of lameness of the right forelimb onset five months ago. The condition progressed slowly to right hemiparesis and proprioceptive ataxia. Clinical and neurological findings included right hemiparesis, proprioceptive ataxia and proprioceptive deficits with decreased flexor reflex and marked atrophy of the right forelimb. Palpation of the right axilla allowed identification of a firm 1 x 3 cm mass, with intense hyperesthesia. Ultrasound examination of the right axilla revealed hypoechoic tubular mass of 1.5 x 3 cm (Figure 1). Once the animal presented signs of ataxia and paresis to the right pelvic limb, it was indicated a computed tomography to observe a possible compression of the spinal cord. An expansive formation was observed in the right brachial plexus between C6-C7 vertebral bodies with isodense characteristic, ring-shaped, with dimensions of 3.82 x 1.56 cm compressing spinal cord. Due to poor prognosis and poor quality of life, euthanasia was elected. The gross changes of the spinal cord were characterized by a firm nodule with irregular surface at the brachial plexus with invasion and compression of C7-C8 spinal cord segment. The microscopic evaluation allowed a diagnosis of malignant sheath nerve tumor. Discussion: Peripheral nerve sheath tumors (PNST) arise from Schwann cells, perineurial fibroblastos or a combination of both cell types that surround axons of peripheral nerves. The diagnosis of PNST is more common in middle-aged to older dogs, of medium to large breeds, as observed in the animal of this report. PNST are more frequently found in the brachial plexus, which results in lameness and/or progressive forelimb paresis associated with neurogenic muscle atrophy. Palpation of a mass in the axillary region is possible in only 29.4% to 37% of cases, which can make diagnosis difficult, however, pain is easily triggered during palpation of the affected area, as noted in the dog of this report. Proprioceptive ataxia and paresis to the hindlimbs occur in 50% of cases and are observed whenever the spinal cord is under compression As signals are insidious, these patients are often evaluated for possible orthopedic conditions, which delays diagnosis of PNST, resulting in a poor prognosis. Ultrasound examination is fast and sensitive for identifying PNST while cross sectional imaging, such as computed tomography are recommended to define the extent of disease and therapeutic planning. However, definitive diagnosis can only be achieved from histopathological examination. The prognosis for animals with PNST is poor, especially when it is associated with invasion of the spinal canal. Early diagnosis, from a detailed clinical examination and imaging exams, must be associated with an aggressive surgical intervention or debulking surgery followed by radiotherapy, in order to improve prognosis, quality of life and survival of these patients.