Here, we describe the first case of a granular cell tumor (GCT) derived from the brachial nerve. Eleven-year-old neutered female Chihuahua presented to the hospital with a bulge from the left neck to the axilla. The dog had a spherical subcutaneous mass on the cervical subcutis, and cytology hinted at adenocarcinoma or neuroendocrine tumor. However, the origin of the tumor remains unknown. During resection of the mass, bleeding was difficult to control owing to the high blood flow, and tumor removal was extremely difficult. The caudal aspect of the mass was attached to the brachial nerve and had to be removed, along with parts of the nerve fibers. The patient\'s postoperative course was fair, but it developed paralysis of the left thoracic limb. Pathology revealed that the mass was positive for S100 and vimentin, and GCT was diagnosed. Non-oral GCTs are extremely rare. The clinical diagnosis of GCT is difficult and is often confirmed histopathologically by excision. Although most cases of GCT are benign, they must be recognized as hemorrhagic, indistinct masses that mimic malignancy. Excision carries the risk of hemorrhage and damage to the surrounding tissues to secure margins.
Descrevemos aqui o primeiro caso de um tumor de células granulares (TCG) derivado do nervo braquial. Uma chihuahua castrada de 11 anos de idade deu entrada no hospital com uma protuberância do pescoço esquerdo até a axila. A cadela apresentava uma massa subcutânea esférica no subcutâneo cervical, e a citologia indicava adenocarcinoma ou tumor neuroendócrino. Entretanto, a origem do tumor permanece desconhecida. Durante a ressecção da massa, foi difícil controlar o sangramento devido ao alto fluxo sanguíneo, e a remoção do tumor foi difícil. O aspecto caudal da massa estava ligado ao nervo braquial e teve de ser removido, juntamente com partes das fibras nervosas. A evolução pós-operatória da paciente foi regular, mas ele desenvolveu paralisia do membro torácico esquerdo. O exame anatomopatológico revelou que a massa era positiva para S100 e vimentina, e o TCG foi diagnosticado. Os TCGs não orais são extremamente raros. O diagnóstico clínico do TCG é difícil e geralmente é confirmado histopatologicamente por excisão. Embora a maioria dos casos de TCG seja benigna, eles devem ser reconhecidos como massas hemorrágicas e indistintas que simulam malignidade. A excisão acarreta o risco de hemorragia e danos aos tecidos circundantes para garantir as margens.

BACKGROUND: Allogeneic hematopoietic stem cell transplantation is a potentially curative treatment for acute myeloid leukemia. However, extramedullary relapse of acute myeloid leukemia can occur after hematopoietic stem cell transplantation, causing treatment failure. Extramedullary relapse rarely involves the peripheral nerves, and it is not influenced by the effect of the graft on leukemia.
METHODS: We report a case of extramedullary relapse of acute myeloid leukemia in the brachial plexus of a 41-year-old woman treated with allogeneic hematopoietic stem cell transplantation (HSCT). Complete hematological remission was confirmed by bone marrow examination 1 month after HSCT, and she developed no major complications immediately after HSCT. The immunosuppressant was discontinued 5 months later. However, 2 weeks after immunosuppressant withdrawal, the patient developed left arm pain and paresthesia, with subsequent development of a mass in the left brachial plexus. She was initially diagnosed with brachial plexus neuropathy because of concomitant graft-versus-host disease. Despite the administration of immunosuppressive agents, the mass continued to enlarge. The biopsy of the lesion revealed leukemic relapse. Thus, the patient was diagnosed with extramedullary relapse and underwent radiotherapy, resulting in tumor shrinkage.
CONCLUSIONS: Extramedullary relapse should be considered a differential diagnosis in post-transplant patients with leukemia presenting with paresthesia.