The consensus was a deliberate revision of the 1998 classification, prompted by advances in the understanding of ET, dystonic tremor, and other monosymptomatic and indeterminate tremors (Louis et al., J Neurol Sci, 2022). Its central structural move was to classify every tremor along two independent axes: Axis 1 captures clinical features (activation condition, distribution, frequency, and any associated signs), and Axis 2 captures etiology. A tremor is then described as an isolated tremor syndrome (tremor as the only sign) or a combined one (tremor plus other neurological features) (Bhatia et al., Mov Disord, 2018). The isolated-versus-combined distinction is the hinge on which ET-plus turns: pure ET is an isolated syndrome, ET-plus sits at the boundary where "isolated" begins to acquire minor company, and a fully combined syndrome (ET-type tremor with unambiguous dystonia or parkinsonism) falls outside the ET label altogether.

Within that structure, ET was re-specified as a particular isolated syndrome rather than a disease entity, and the ET-plus term was introduced to name the very common situation in which the ET phenotype coexists with minor additional signs that are not sufficient to invoke a different diagnosis. The conceptual shift is important: the framework treats "essential tremor" less as a single disease and more as a clinically defined syndrome that likely subsumes several etiologies — a point long argued in the literature on the heterogeneity and pitfalls of the ET label (Espay et al., Mov Disord, 2017).

The operational definitions are specific. Essential tremor is an isolated tremor syndrome of bilateral upper-limb action tremor, of at least 3 years' duration, with or without tremor in other locations (head, voice, or lower limbs), and crucially without other neurological signs such as dystonia, ataxia, or parkinsonism (Bhatia et al., Mov Disord, 2018).

ET-plus is that same syndrome plus additional soft signs of uncertain clinical significance:

The defining feature of the qualifying signs is precisely that they are mild, soft, or "questionable" — a mild rest tremor that does not amount to parkinsonism, a suggestion of dystonic posturing that does not meet criteria for dystonia, a subtle tandem-gait abnormality, or mild cognitive change. That deliberate softness is both the point of the category and the source of the argument about it.

ET-plus is not an occasional refinement; it accounts for a large fraction of what has traditionally been diagnosed as ET. In a reclassification of 665 clinically confirmed ET-syndrome patients, 274 were classified as ET and 391 (approximately 59%) as ET-plus, with rest tremor the most prevalent qualifying soft sign (Peng et al., J Neurol, 2022). A tertiary-center registry of non-parkinsonian tremors found a comparable split — of patients meeting ET criteria, roughly half were pure ET and half ET-plus (Pandey et al., Tremor Other Hyperkinet Mov, 2023).

The practical implication is that applying the 2018 criteria reclassifies a substantial share of a typical ET clinic population, and that the presence of a mild rest tremor — a sign many clinicians previously tolerated within an ET diagnosis — is now the most common trigger for the ET-plus designation.

Beyond its definition, the reclassification data suggest ET-plus is not a random relabeling. Compared with pure-ET patients, ET-plus patients were older, had an older age at onset and a longer disease duration, scored higher on tremor-severity measures and lower on cognitive testing, and more often had depressive or anxiety symptoms (Peng et al., J Neurol, 2022). In that series, rest tremor and questionable cerebellar signs in particular were associated with greater tremor severity.

This profile is compatible with two non-exclusive readings. One is that ET-plus marks a more advanced or severe phenotype — a longer-standing, heavier-burden tremor that has accrued additional signs over time. The other is that it enriches for cases with a distinct or additional underlying process that the soft signs betray. The 2018 framework deliberately makes no etiological claim: ET-plus is an Axis-1 descriptor, not an Axis-2 diagnosis, and whether it is a stage, a severity band, or a marker of a separate biology remains open (Welton et al., Nat Rev Dis Primers, 2021).

The clinically consequential edge of ET-plus is that its qualifying signs sit on the same spectrum as the cardinal features of other tremor syndromes — and telling a stable soft sign from an early declaration of a different disease is the real diagnostic work. A mild rest tremor, the most common ET-plus qualifier, is the clearest example: in an older patient it raises the question of early Parkinson's disease, and the distinction turns on whether other parkinsonian features (bradykinesia, rigidity, a re-emergent rather than simple rest tremor) are absent or merely not yet apparent (van de Wardt et al., J Neurol Neurosurg Psychiatry, 2020). Likewise, "questionable dystonic posturing" abuts genuine dystonic tremor, and a subtle tandem-gait sign abuts cerebellar disease.

This is why ET-plus is best treated as a flag for surveillance rather than a closed diagnosis. The soft sign that qualifies a patient today may remain static for years — consistent with ET-plus as a phenotype — or may, over time, evolve into the full syndrome it hinted at, at which point the Axis-1 label gives way to an Axis-2 diagnosis. Re-examining the questionable signs at intervals, rather than fixing them at first assessment, is the practical safeguard against both premature closure and missed evolution (Bhatia et al., Mov Disord, 2018).

The argument in favor is primarily one of precision. Proponents — including members of the original task force — hold that separating pure ET from ET-plus reduces the heterogeneity that has long plagued ET research, and that a cleaner phenotype improves the chances of finding reproducible imaging, genetic, and pathological correlates (Latorre et al., J Neurol Sci, 2022). On this view, the "soft signs" are not noise to be discarded but information: a patient with a mild rest tremor or a subtle gait sign is meaningfully different from one without, and pooling them has historically muddied study cohorts. The two-axis structure also brings ET into line with the rest of tremor nosology, giving a systematic language for the many tremors that sit between classic ET and other syndromes (van de Wardt et al., J Neurol Neurosurg Psychiatry, 2020).

The critique is equally substantive. Its core is that the qualifying signs are poorly operationalized and of uncertain inter-rater reliability: "questionable dystonic posturing" and "mild memory impairment" are, by construction, subjective judgments, and the boundary between a tolerable soft sign and a disqualifying one is not sharply drawn (Louis et al., J Neurol Sci, 2022). A category that captures roughly half of all patients yet rests on such thresholds risks becoming a heterogeneous catch-all rather than a discriminating one — and, critically, ET-plus has no established prognostic or therapeutic consequence, so a clinician who applies the label does not thereby change what they offer the patient.

These concerns are not new to the ET-plus era; they extend a longer argument that "essential tremor" has always over-lumped distinct conditions and that its diagnostic pitfalls are considerable (Espay et al., Mov Disord, 2017; Quinn et al., Mov Disord, 2011). From this vantage, ET-plus is a reasonable acknowledgement that ET is heterogeneous, but not yet a solution to it — a useful research flag more than an actionable clinical diagnosis.

For practice, the reasonable posture is to apply the classification carefully but hold it lightly. Documenting whether a patient meets ET or ET-plus criteria — and which soft sign qualifies them — adds useful phenotypic detail and flags patients who warrant closer follow-up for evolution toward a defined syndrome (a mild rest tremor that later declares itself as parkinsonism being the paradigm case). At the same time, an ET-plus label should not be over-read: it does not, on current evidence, mandate different treatment or imply a worse prognosis, and the "questionable" signs should be re-examined over time rather than fixed at first assessment (Wagle Shukla, Continuum, 2022).

For research, the value proposition is clearer but still provisional: separating pure ET from ET-plus is worthwhile precisely because it may resolve some of the field's reproducibility problems — but only if the soft signs are captured with standardized, reliable methods. The defensible summary is that the 2018 reclassification was a real conceptual advance in treating ET as a syndrome rather than a single disease, that ET-plus meaningfully describes a large and clinically distinguishable subgroup, and that whether it earns the status of a distinct entity awaits the biomarker and longitudinal data the classification was designed to make possible.