A Non-Neurodegenerative REM Parasomnia with Immersive Dreaming and Dream-Reality Confusion: A Case Report

Nazanin Aghajan Biabani¹Martina Mulas^1,2Carlotta Mutti³Sean Higgins⁴Katarina Ilic^1,5Joshua Benson⁴Ana Santic^1,6Valentina Gnoni⁷Panagis Drakatos^1,4,8Andrea Romigi⁹Alexander D Nesbitt^1,10Sharon Linda Naismith¹¹Carlos Schenck¹²David O'Regan^1,4,8Monica Puligheddu²Ivana Rosenzweig^1,4*

• ¹Sleep and Brain Plasticity Centre, Department of Neuroimaging, Institute of Psychiatry, Psychology and Neuroscience (IoPPN), King's College London, U.K, London, United Kingdom
• ²Sleep Disorder Centre, Department of Medical Sciences and Public Health, University of Cagliari,Italy, Cagliari, Italy
• ³Sleep Disorders Centre, Department of Medicine and Surgery, Parma University Hospital and Mario Giovanni Terzano Interdepartmental Centre for Sleep Medicine, University of Parma, Parma, Italy, Parma, Italy
• ⁴Sleep Disorders Centre, Guy's and St Thomas’ NHS Foundation Trust, London, U.K, London, United Kingdom
• ⁵BRAIN Centre, Institute of Psychiatry Psychology and Neuroscience, King’s College London, London, UK, London, United Kingdom
• ⁶Department for Sleep Disorders, Psychiatric Clinic Vrapce, Zagreb, Croatia, Zagreb, Croatia
• ⁷Centre for Neurodegenerative Diseases and the Aging Brain, Department of Clinical Research in Neurology, University of Bari ‘Aldo Moro’, Tricase, Italy, Bari, Italy
• ⁸School of Basic and Medical Biosciences, Faculty of Life Science and Medicine, King’s College London, London, UK, London, United Kingdom
• ⁹Università Telematica Internazionale UNINETTUNO, Rome, Italy, Roma, Italy
• ¹⁰Department of Neurology, Guy's and St Thomas’ NHS Foundation Trust, London, U.K., London, United Kingdom
• ¹¹Healthy Brain Ageing Program, The Brain and Mind Centre, University of Sydney, Australia, Sydney, Australia
• ¹²Minnesota Regional Sleep Disorders Center, and Departments of Psychiatry, Hennepin County Medical Centre and University of Minnesota Medical School, Minneapolis, USA, Minneapolis, United States

Background: REM sleep behaviour disorder (RBD) is characterised by loss of normal muscle atonia during REM sleep, often associated with dream enactment behaviours, and is typically a prodromal neurodegenerative condition in middle-aged and older adults. However, emerging case reports and case series suggest that not all RBD presentations follow this trajectory, particularly in younger individuals. Case Presentation: A case of seven-year history of vivid, immersive dreaming perceived as continuous with waking life, accompanied by persistent dream-reality confusion, is described. The patient frequently engaged in reality-testing behaviours and reported significant cognitive fatigue. Video-polysomnography confirmed REM sleep without atonia and a concordant dream re-enactment episode. Neuropsychiatric evaluation ruled out dissociative or psychotic disorders, and no evidence of neurodegenerative disease was observed. Conclusion: This presented case illustrates a potentially distinct, non-neurodegenerative REM parasomnia phenotype that underscores the need to expand current parasomnia classifications to better capture the diverse cognitive and metacognitive dimensions of REM sleep disorders. Moreover, potential mechanisms underlying the main features of this case, including immersive dreaming and persistent dream-reality confusion, are discussed in relation to hypothesized dysfunction in melanin-concentrating hormone (MCH) signalling.