Background:

Narcolepsy is a neurologic sleep disorder, in humans characterized by excessive and recurrent daytime sleepiness, rapid eye movement in the beginning of the sleep, in association with hypnagogic hallucinations and sleep paralysis, with or without cataplexy. In dogs, the characteristic symptom is cataplexy and narcolepsy exists in two forms, one genetic and one acquired. This article describes one case of narcolepsy as a symptom due to an adenohypophysis tumor. Case Dog presenting progressive signs of appetite loss, incoordination and constant falling. At clinical evaluation, the dog presented cachexia, hipocolored mucosae and compulsively walking in circles to the right, the four limbs collapsed from physical exhaustion, remaining in a narcoleptic state. Complementary exams, like x-ray, ultrasonography, hemogram and biochemical examination did not show significant alterations. The patient was hospitalized for recovery of general status and corticoid treatment was initiated, but after two days it died. Necropsy reported that the cause of death was 180º gastric torsion and adrenals presented diffuse and marked enlargement of the cortical layer, 1.5 cm diameter neoplasia at the base of the brain and 0.5 cm diameter cavitation in the cerebral parenchyma. In the microscopic examination, adrenals were hyperplastic at the cortical region and there was round cell proliferation, with some basophilic cytoplasm and others more eosinophilic at the hypophysis with parenchyma nervous tissue invasion, reaching the diagnosis of macroadenoma of adenohypophysis chromophil cells.

Discussion:

secondary or symptomatic narcolepsy is not commonly described in animals, with just one case report being found in the literature, in which the patient presented narcolepsy-cataplexy secondary to post-vaccination encephalitis. In humans, it has been reported in cases of hypothalamic pathologies, like Niemann-Pick type C disease, neoplasia, trauma, vascular issues, post-encephalitis, agenesis of the corpus callosum, sarcoidosis, neurocysticercosis and limbic encephalitis. In the described case, probably, there was an infi ltration from the hypophysis macroadenoma to the adjacent tissues, causing destruction and compression of hypothalamic neurons. The hypophisary macroadenomas, with nervous symptoms, occur due to tumor dorsal extention, dorso-caudal direction, comprising and invading the hypothalamus and the third ventricle. The most common signs are apathy, ataxy, behavioral changes, sight reduction and facial paralysis, being some of these symptoms observed in the present case. According to several reports in humans, the hypocretin levels (neurotransmitter which presents the function of sleep regulation, alertness and food intake) is used to diagnose narcolepsy, however, in case of secondary narcolepsy, the neurotransmitter can or not be decreased. Cases in which it had normal amount, the authors based on clinical signs concluded that the hypocretinergic system (hypocretin-1 and 2, and its respective receptors) would be compromised. The patient died before the hypocretin dosage was performed to confirm secondary narcolepsy. For that, it would be necessary to collect cephalorachidian fluid, under sedation, but the dog was not in adequate physical condition to go under such procedure. Because of that, it was concluded that, by symptomatology, its hypocretinergic system was affected, because the location of the tumor lesion is similar to other cases reported in humans.