1357 Clinical Crossroads: The Dilemma Between Idiopathic Hypersomnia and Non-Hydrocephalic Symptomatic Pineal Cyst Syndrome

Abstract Introduction The diagnostic process in clinical practice is complex. Many diagnoses rely on objective, quantifiable findings, while others are reached only after excluding all other reasonable explanations. Challenges arise when a diagnosis of exclusion is made but remains uncertain or contested, especially when a condition that is not well established may represent the true underlying diagnosis. In this discussion, we present the case of a patient who met the diagnostic criteria for idiopathic hypersomnia (IH); however, the suitability of this diagnosis is challenged by the possibility that Non-Hydrocephalic Symptomatic Pineal Cyst Syndrome (nhSPCS) may better explain the clinical presentation. Despite emerging evidence, nhSPCS remains a condition that is not well established. Report of case(s) A 25-year-old woman with no notable medical history presented with three years of excessive daytime sleepiness (despite 13-16 hours of sleep daily), lightheadedness, restless sleep, and cognitive difficulties. The patient was evaluated with PSG and MSLT, revealing short sleep latency (4 minutes) but no sleep onset REM or evidence of narcolepsy. The findings supported IH after other medical causes, were excluded. Neurology was consulted due to concerns for migraine-like symptoms, dizziness, fatigue, nausea, vomiting, fainting, and possible vasovagal syncope. Neurological exam was intact, but brain MRI revealed a 1.7x0.8x1 cm pineal gland cyst with calcifications and minor hemorrhagic features, but no hydrocephalus. Differential diagnoses included pineocytoma or pineal cyst, possibly suggesting nhSPCS as a potential explanation for the patient’s hypersomnia and other symptoms unrelated to sleep. Conclusion This case highlights the critical need for maintaining diagnostic flexibility when assessing central disorders of hypersomnolence. While idiopathic hypersomnia is typically a diagnosis of exclusion, the presence of coexisting structural abnormalities, such as a considerable large, complex pineal cyst, should prompt clinicians to reconsider the presumed etiology of hypersomnolence. Recognizing the potential overlap between IH and nhSPCS may enhance diagnostic accuracy, inform more targeted treatment strategies, and mitigate the risk of misattributing symptoms to isolated sleep pathology when a broader neuroanatomical process may be involved. Although the diagnosis of nhSPCS remains a subject of debate, this case may contribute to a better understanding of its symptoms and improve the assessment of sleep disorders. Support (if any)