Rethinking Burning Mouth Syndrome: Toward a multidimensional classification of oral dysaesthetic and perceptual disorders in ICHD-4

Introduction

Burning Mouth Syndrome (BMS) is traditionally defined as a chronic idiopathic condition characterized by persistent oral burning sensations in the absence of identifiable local or systemic causes. Both the International Classification of Orofacial Pain (ICOP 2020) ¹ and the International Classification of Headache Disorders, 3rd Edition (ICHD-3) ² place burning as the cardinal and essentially mandatory symptom. Yet clinical reality tells a different story. A substantial proportion of patients present with persistent oral discomfort that is not burning in quality: tingling, foreign body sensation, dysgeusia, xerostomia, oral dysmorphia, or globus pharyngeus, often in combination. These individuals remain diagnostically invisible under current criteria, despite comparable suffering and functional impairment. This editorial highlights potential conceptual limitations of existing classifications and considers Oral Dysaesthetic and Perceptual Disorder (ODPD), within the broader conceptual domain of oral dysaesthesia (OD), as a tentative, multidimensional framework that may help further characterize this underrecognized spectrum.

Limitations of current classifications

The evolution of BMS nosology reflects a gradual but incomplete broadening of diagnostic construct. As early as the 19th century, historical medical literature documented a spectrum of oral sensations well beyond burning. Kaposi's glossodynia exfoliativa (1885) described symptoms including “tingling, burning, scalding, roughness, numbness, heaviness, and other paresthesias”. ³ This clinical presentation has also been documented in later studies, in which patients frequently reported symptoms beyond burning, such as dry mouth and taste disturbances. The clinical heterogeneity of idiopathic oral symptoms was thus recognized long before any formal classification existed, and early proposals such as the Complex Oral Sensitivity Disorder attempted to capture this multiplicity. ⁴ Yet as formal classification systems emerged, the diagnostic lens progressively narrowed around burning as a defining feature.

The ICHD-2 (2004) formalized the term BMS and required daily burning pain persisting for more than two hours over at least three months. Associated symptoms such as dysgeusia and xerostomia were relegated to comments. The ICHD-3 (2018) took a step forward by explicitly acknowledging that dysaesthetic sensations may accompany burning. Yet, crucially, burning remains an obligatory diagnostic criterion. A patient experiencing chronic, debilitating tingling, pruritus, or foreign body sensation without any burning component simply does not qualify. This highlights a conceptual inconsistency: the classification acknowledges clinical heterogeneity in its descriptive text yet fails to translate that acknowledgment into its operative criteria. The ICOP 2020 follows the same logic, adding a subdivision for cases with or without somatosensory changes, but without departing from the burning-centric model.

The ICOP-2 Steering Committee has itself acknowledged that discussion is ongoing regarding the validity of idiopathic pain conditions with or without somatosensory abnormalities, and that the evolving concept of nociplastic pain will need to be addressed in the upcoming revision, ⁵ underscoring that even the architects of the current classification recognize its limitations in this domain.

These limitations are further supported by findings from an international Delphi study (2021), ⁶ which demonstrated substantial variability in definitions and diagnostic criteria for BMS across studies, contributing to heterogeneity in patient selection and limiting the interpretability of research findings. In the same study, expert consensus supported revising both nomenclature and diagnostic criteria, including a preference for the term “burning mouth disorder,” to improve clarity and clinical applicability, highlighting the lack of a unified and operational definition.

The consequence is a substantial diagnostic gap: patients without burning, but with equally chronic, distressing, and functionally impairing oral symptoms, do not meet current criteria. They face prolonged diagnostic delays, often exceeding 30 months, multiple specialist referrals, and lack of access to evidence-based care. ⁷ The narrowness of definitions has become a barrier to recognition rather than a tool for clarity.

Suga and colleagues recently highlighted this issue in their letter “Toward ICHD-4: Proposing a Broader Diagnostic Framework for Burning Mouth Syndrome”, advocating for the inclusion of dysaesthetic descriptors such as stinging or tingling to better reflect clinical reality. ⁸ Their proposal represents meaningful progress.

In line with this conceptualization, OD is defined as a chronic condition characterized by persistent alterations in oral sensation, perceived by patients as abnormal or unpleasant, in the absence of an identifiable local or systemic cause. As recently reviewed, OD encompasses a range of idiopathic oral sensory symptoms, with BMS representing the most common and best-defined phenotype.

However, restricting classification to dysaesthetic symptoms alone may be insufficient, as a subset of patients presents with perceptual distortions that are not fully captured within the current conceptualization of dysaesthesia.

The ODPD framework

In this context, the concept of ODPD may offer a framework to better capture these clinical presentations. This model proposes that idiopathic oral symptoms may be understood along two complementary dimensions. The dysaesthetic dimension encompasses abnormal and often unpleasant sensations, including burning, tingling, paresthesia-like sensations, pruritus, hypoesthesia, and allodynia, occurring without any apparent physical cause, whether spontaneous or evoked, and reflecting dysfunction of sensory pathways. These sensations may be persistent, debilitating, and significantly impact daily functioning.

In contrast, the perceptual dimension refers to an impairment in the ability to accurately interpret sensory information, particularly related to immediate sensory experiences, without necessarily involving an abnormal sensory input. This results in distortions or misinterpretations of sensory stimuli, reflecting altered central processing of sensory inputs and leading to difficulties in interacting with the environment. Examples include oral dysmorphia, phantom taste sensations, dysosmia, subjective halitosis, foreign body sensation, occlusal dysaesthesia, oral dyskinesia, and globus pharyngeus.

Importantly, the inclusion of a perceptual dimension is not intended to imply a primary cognitive or psychiatric etiology or to contradict the neuropathic nature of BMS. Rather, the term “perceptual” is used in its physiological sense, referring to the processing and interpretation of sensory stimuli.

Within this perspective, perceptual disturbances may be understood as distorted representations of oral structures or functions, rather than as unpleasant sensory symptoms alone.

While some patients present predominantly with one profile, others exhibit overlapping features that do not fit neatly within existing diagnostic frameworks. In this context, symptoms such as dysgeusia, globus pharyngeus, and foreign body sensation may display hybrid characteristics, reflecting both altered sensory signaling and higher-order perceptual processing, thereby highlighting the limitations of strictly unidimensional models. ⁹ These overlapping presentations may reflect shared alterations in central sensory processing, while also potentially involving partially distinct pathophysiological mechanisms, supporting a multidimensional rather than strictly unidimensional conceptualization.

Consistent with this viewpoint, Suga et al., ¹⁰ in the subsequent reply, explicitly endorsed the distinction between dysaesthetic and perceptual domains as essential to capturing the full clinical spectrum, while emphasizing appropriate caution in formalizing such distinctions without robust empirical validation. In their letter, they describe symptoms such as oral dysmorphism and foreign-body sensations as cenesthopathic manifestations, in line with the original definition proposed by Dupré. Conceptually, these phenomena overlap with what we define as alterations within a perceptual domain of oral sensory processing. While this terminology has been adopted in prior literature, its application remains conceptually heterogeneous and may overlap with psychiatric classifications (e.g., somatic-type delusional disorders), warranting caution. Accordingly, in the present model, these symptoms are more conservatively conceptualized within a perceptual dimension of altered oral sensory processing, rather than as discrete diagnostic entities.

Accordingly, ODPD is proposed as a descriptive and hypothesis-generating model to better conceptualize patients presenting with symptom profiles not adequately captured by current criteria, rather than as a standalone diagnostic entity. Within this framework, BMS remains the most well-defined phenotype, while ODPD serves to contextualize the heterogeneity of idiopathic oral sensory symptoms not fully captured by current burning-centric definitions.^7,9

At the same time, caution is warranted to avoid overexpansion of diagnostic boundaries. Any broader conceptual framework should not be interpreted as a standalone diagnosis or used indiscriminately for unexplained oral symptoms, but rather as a descriptive approach to improve clinical characterization while preserving established diagnostic pathways and distinctions from psychiatric or functional disorders.

Implications and the way forward

Refining current classification frameworks carries important clinical and ethical implications.

Accurate diagnostic allocation enables precise phenotyping, reduces unnecessary investigations, and supports the development of targeted, personalized interventions. Patients who do not meet current diagnostic criteria experience comparable psychological comorbidity and functional impairment to those who meet current BMS definitions; they deserve equivalent recognition and care. ⁷

Concurrently, we acknowledge that the evidence supporting expanded conceptual models, including ODPD, remains preliminary and requires validation across diverse populations and settings before consideration for inclusion in future ICHD and ICOP revisions. Notably, the ODPD framework has been derived from a single-institution case–control study, which may limit its generalizability. ⁷ As such, these models may serve as hypothesis-generating frameworks to inform refinement of existing criteria rather than immediate changes to classification systems.

The planned alignment between ICOP-2 and ICHD-4, both tentatively scheduled for publication in 2029, ⁵ represents a unique and time-sensitive opportunity to re-evaluate current classification frameworks within a more integrated, interdisciplinary perspective.

Within this framework, the distinction between dysaesthetic and perceptual dimensions may help inform ongoing discussions within the ICOP-2 Steering Committee and support the development of a more harmonized taxonomy.

An alternative approach would be to refine existing criteria by assigning differential weight to relevant symptom domains rather than introducing a separate framework. This represents a reasonable strategy. Importantly, distinguishing between dysaesthetic and perceptual components may also support such refinements by identifying symptom domains that are not adequately captured in current classifications.

From a clinical perspective, framing these presentations within a broader conceptual model may enable more nuanced characterization of symptom profiles, inform therapeutic decision-making, and support tailored assessment and management strategies based on the predominant symptom pattern. The lack of a consistent and inclusive nomenclature continues to limit systematic study and the development of targeted interventions.

In this setting, ODPD provides a structured approach to describe these symptom domains, potentially facilitating more standardized research and, over time, more individualized management. However, further research is needed to better delineate these domains and clarify their underlying neurobiological mechanisms.

Finally, we call for the establishment of a unified classification framework bridging the ICHD and ICOP. The current disciplinary gap, with neurologists relying on ICHD criteria and orofacial pain specialists on ICOP, has produced fragmented diagnostic approaches and inconsistent terminology. As chronic oral dysaesthetic and perceptual disorders inherently span neurology, dentistry, pain medicine, and psychiatry, a consensus-driven interdisciplinary panel should develop harmonized criteria applicable across specialties.

The history of BMS demonstrates how rigid, symptom-anchored definitions can perpetuate patient marginalization. ³ Recognizing the full heterogeneity of chronic idiopathic oral disorders and formally incorporating this multidimensional perspective into international classification systems is both a scientific necessity and a moral imperative.