Tic disorders and allergic diseases: mechanistic links and the impact of allergy management - a narrative review.

Tic disorders are childhood-onset neuropsychiatric conditions that frequently co-occur with allergic diseases, including asthma, allergic rhinitis, and atopic dermatitis. This narrative review maps the current clinical and mechanistic evidence linking allergic conditions to tic disorders and evaluates whether allergy focused interventions may modify tic severity. Across multiple epidemiological studies, allergic diseases are reported more often in children with tic disorders than in controls. However, direct clinical evidence supporting a canonical "central allergic response" within the brain (e.g., IgE-driven allergic effector mechanisms in the CNS) in primary tic disorders remains limited. The available literature instead more strongly supports indirect, peripheral, brain directed pathways. Peripheral inflammatory mediators may modulate the neurovascular unit and glial reactivity, thereby influencing cortico-striato-thalamo-cortical circuit excitability. Histamine, acting as both an immune mediator and a neuromodulator, may further intersect with dopaminergic signalling relevant to tic expression. In parallel, allergy related symptom burden, particularly sleep disruption and psychological stress, may contribute to tic exacerbation. Observational studies suggest that controlling allergic symptoms can be associated with reduced tic severity in some individuals, although certain anti allergic agents have been reported to coincide with tic worsening in selected cases. Overall, current findings support a model in which allergic conditions influence tic disorders primarily via immune signalling and symptom burden rather than through a direct central allergic mechanism. Allergy assessment and management may be considered in selected patients, but mechanistic studies and controlled trials are needed to clarify causality and guide evidence-based care.