Rare neuropsychiatric syndromes at the interface of neurology and psychiatry: a narrative review of diagnostic pitfalls and clinical lessons

Abstract Rare neurological and neuropsychiatric syndromes, although individually uncommon, collectively contribute to misdiagnosis, avoidable investigations, and occasional preventable harm. Many of these conditions sit at the interface of neurology and psychiatry and are vulnerable to diagnostic overshadowing, in which clinically unfamiliar presentations are dismissed as functional or psychiatric. This narrative review examines six clinically significant entities that exemplify this problem: Beauty Parlor Stroke Syndrome (BPSS), Alice in Wonderland Syndrome (AIWS), Alien Hand Syndrome (AHS) and Alien Limb Phenomenon (ALP), Exploding Head Syndrome (EHS), Cotard’s Delusion (CD), and the syndrome of transient Headache and Neurological Deficits with cerebrospinal fluid Lymphocytosis (HaNDL). These conditions were selected because each is uncommon, each is reproducibly misclassified in routine practice (typically as a psychiatric, functional, or benign positional disorder), and each has a defined neurological substrate with implications for management. We provide a narrative synthesis of published literature, drawing on case series, cohort studies, narrative reviews, and consensus criteria such as the International Classification of Headache Disorders, 3rd edition (ICHD-3) for HaNDL. BPSS is discussed as a mechanical cause of vertebrobasilar ischaemia, classically following cervical hyperextension at a salon basin, in which symptoms are commonly attributed initially to benign positional vertigo or anxiety. AIWS is described as a perceptual disorder characterised by dysmetropsia and altered body schema, most often associated with migraine in adults and with viral infection (particularly Epstein–Barr virus) in children; reported lifetime prevalence in adult migraineurs varies between studies in the approximate range of 16–19%, with higher rates in those with migraine with aura. The distinction between AHS, typically of acute callosal or frontal medial origin, and ALP, more typically associated with parietal dysfunction in corticobasal syndrome, is clarified. EHS is presented as a benign sensory parasomnia that mimics serious intracranial events. Cotard’s delusion is described as a nihilistic delusion most often arising in severe depression with psychotic features and carrying a significant risk of self-neglect and suicide. HaNDL is framed according to ICHD-3 criteria as an important stroke and encephalitis mimic. We discuss cross-cutting diagnostic pitfalls, summarise recommended investigations and management, and outline the limitations of the current evidence base, which is dominated by case reports and small case series. We also briefly consider the limited but emerging role of digital symptom search and artificial-intelligence tools as adjuncts to clinical reasoning, not as substitutes for it.