A 3-year-old, male, entire, German wirehaired pointer dog was presented with a 2-year history of paroxysmal episodes of collapse associated with reduced levels of consciousness. A magnetic resonance imaging study identified a single, ill-defined, non-contrast-enhancing, intra-axial mass lesion involving the hypothalamus. Cerebrospinal fluid levels of hypocretin (orexin) neuropeptide were below normal, consistent with a disease process affecting the sleep–wake cycle. The dog was diagnosed with suspected acquired narcolepsy secondary to a presumptive hypothalamic hamartoma. Treatment with imipramine resulted in reduced frequency and severity of the episodes.</p
