BackgroundInsulinomas are rare neuroendocrine tumors that typically present with hypoglycemic crises. Peripheral neuropathy is an uncommon complication of insulinoma. Most clinicians expect peripheral neuropathy symptoms to reverse completely after the insulin-secreting tumor is resected, but this may be a misassumption.Case reportWe report a case of a 16-year-old Brazilian boy with clonic muscle spasms of the lower limbs for almost one year. Disabling paraparesis and confusional episodes had progressively set in as well. There were no sensorial abnormalities in the lower limbs, upper limbs or cranial nerves. An electromyography revealed a motor neuropathy of the lower limbs. The diagnosis of insulinoma was established as serum insulin and C-peptide concentrations were inappropriately normal during spontaneous episodes of hypoglycemia. Following a normal abdominal magnetic resonance scan, the imaging work-up continued with an endoscopic ultrasound, which localized the tumor at the pancreatic body-tail transition. Once localized, a prompt surgical removal (enucleation) of the tumor was undertaken, leading to an immediate and complete resolution of hypoglycemia. The time length between the onset of symptoms and tumor resection was 15 months. After surgery, the symptoms of peripheral neuropathy of the lower limbs showed a slow and only partial improvement. At a two-year follow-up after surgery, although being able to lead a normal and productive life, the patient still reported symptoms of reduced muscular strength in the lower limbs and a new electroneuromyography analysis showed chronic denervation and reinnervation in the legs’ muscles—indicating chronic neuropathic injury.ConclusionThe events of this case reinforce the importance of an agile diagnostic work-up and spry definitive treatment for patients with this uncommon disease, enabling the cure of neuroglycopenia before permanent bothersome complications ensue.