Cluster analysis of the Yale Global Tic Severity Scale (YGTSS): symptom dimensions and clinical correlates in an outpatient youth sample

Abstract

Tic disorders are heterogeneous, with symptoms varying widely both within and across patients. Exploration of symptom clusters may aid in the identification of symptom dimensions of empirical and treatment import. This article presents the results of two studies investigating tic symptom clusters using a sample of 99 youth (M age = 10.7, 81% male, 77% Caucasian) diagnosed with a primary tic disorder (Tourette's disorder or chronic tic disorder), across two university-based outpatient clinics specializing in tic and related disorders. In Study 1, a cluster analysis of the Yale Global Tic Severity Scale (YGTSS) identified four symptom dimensions: predominantly complex tics; simple head/face tics; simple body tics; and simple vocal/facial tics. In Study 2, these clusters were shown to be differentially associated with demographic and clinical characteristics. Findings lend support to prior research on tic phenomenology, help to organize treatment goals, and suggest symptom dimensions of tic disorders for further evaluation.

Fig. 1

Rescaled dendrogram of agglomerative hierarchical cluster analysis using Ward’s method of 46 YGTSS symptom checklist items from 99 primary tic disorder participants from two sites (UCLA and UWM). Text colors indicate clustered symptoms. Symptoms were classified into a cluster when: (a) their dendrogram lines converged within a 10-unit window on the dendrogram cluster distance axis; and (b) the convergence occurred before 50 (0=individual symptoms, 100=unitary cluster of all symptoms)

Fig. 2

Lines represent quadratic trends