Transient environmental effects on tic severity
Tic suppression
Sensory phenomena and premonitory urges
"In summary, being aware of signals for emerging tics facilitated self-initiated tic suppression, while ruminative tic-associated sensations did not." \citep{32719621}
Sensory hypersensitivity is a frequent feature in patients with TS and should not be associated uniquely or primarily with autism spectrum disorder. In 34 adults with TS, Isaacs et al. confirm what had previously been described mostly in youth with TS, and further show further show that sensory hypersensitivity is independently associated with obsessive-compulsive symptom severity \citep{33173296}. By the same group a comprehensive review on this topic with an accent on pathophysiology of sensory processing dysfunction in TS and associated disorders \citep*{Isaacs2020} .
A revised version of the PUTS (Premonitory Urges for Tic Disorders Scale - PUTS-R) was proposed by Baumung et al., with slight rephrases compared to the original, and dividing it into two subscales regarding urge severity and urge quality \citep{Baumung2021}. Also, the psychometric properties of the original scale were tested in a very large cohort of children (n=658, subdivided into three age groups: 3 to 7 years, 8 to 10 years, 11 to 16 years)) within the EMTICS study. Contrary to previous findings, the PUTS also displayed good internal reliability in children under the age of 10. Also, in children 11 years or older, sensory phenomena related to tics and mental phenomena observed in obsessive-compulsive disorder could be distinguished. The authors conclude that questionnaires assessing premonitory urges might need to be age-specific \citep{Openneer2020}.
Other
Emotional dysregulation is frequently observed in TS and thought to be related to the co-occurence of ADHD, eventually predisposing to explosive outbursts. However, it has has so far been mostly assessed in parent-reported questionnaires. Using an observational measure, Hagstrom observational measure, Hagstrom et al. directly examined children with TS only, ADHD only, TS+ADHD, and controls. Emotional dysregulation was clearly dependent on the presence of ADHD and could not be observed in TS only \citep{Hagstrøm2021}.
A well-written and comprehensive review on one of the foremost therapeutic challenges in TS, i.e., rage attacks: many questions remain open and much work needs to be done work needs to be done \citep{Conte2020a}. On this topic, Müller-Vahl et al. propose a revised version of their Rage Attack Questionnaire for adults, this becoming the RAQ-R. Testing this new tool in 127 patients with TS (compared to 645 controls), it was found that rage attacks correlated with and ADHD but, interestingly, could also be observed in "TS only" patients \citep{Müller-Vahl2019}.
Aggressive symptoms in youths with TS (n=47, compared to 32 controls) appear to correlate with the severity of ADHD; overall, there was - somewhat surprisingly - no difference between the TS and the control group. Note, whoever, that agression and rage attacks may be correlated but are not identical entities \citep{Benaroya-Milshtein2020}.
Two up-to-date and complete review of sleep disorders in TS, covering both adults and children \citep{Jiménez-Jiménez2020}\citep{Hibberd2020}.
"Executive function in children with Tourette syndrome and attention-deficit/hyperactivity disorder: Cross-disorder or unique impairments?" \citep{31901563}
Symptoms suggesting disinhibition in TS \citep{Kurvits_2020}.
Review of self-injurious behavior in TS \citep*{32205150}.
Large study (N=720) comparing autistic and compulsive phenomena in children with a clinical diagnosis of either TS or ASD \citep{32443587}. (Need to read it.)
Aggressive symptoms in children with tics \citep{31396706}
Etiology
Genetics
Epigenetics
Environmental risk factors
A monumental and definitive review (for the time being) on the immunology (immune pathways, neuroinflammation, microbiome) of brain development in general and TS in particular by one of the foremost specialists in the field \citep{Martino2020}.
Pathophysiology
Animal models
"The Sapap3-knockout mouse model manifests a spectrum of repetitive behaviours" \citep{Lamothe_2020}
Title: "Metastable attractors explain the variable timing of stable behavioral action sequences" abstract: "Here, we focus on the observation that the timing of self-initiated actions shows large variability even when they are executed in stable, well-learned sequences. Could this mix of reliability and stochasticity arise within the same circuit? We trained rats to perform a stereotyped sequence of self-initiated actions and recorded neural ensemble activity in secondary motor cortex (M2), which is known to reflect trial-by-trial action timing fluctuations. Using hidden Markov models we established a robust and accurate dictionary between ensemble activity patterns and actions. We then showed that metastable attractors, representing activity patterns with the requisite combination of reliable sequential structure and high transition timing variability, could be produced by reciprocally coupling a high dimensional recurrent network and a low dimensional feedforward one." \citep{Recanatesi_2020} (emphasis added)
Circuit in birdsong vocal and motor learning (doi: 10.1101/2020.03.14.991042)
Inhibiting parvalbumin-containing GABAergic neurons in a prefrontal-striatal circuit previously implicated in excessive habit generation (persistent rodent grooming to a tone before a drop of water on the face) impairs feedforward inhibition \citep{32029441} (reviewed in TAA conference talk 2021-05-14)
Pathological studies
Electrophysiology
Neuroimaging studies
"Alterations in cerebellar grey matter structure and covariance networks in young people with Tourette syndrome" \citep{Sigurdsson_2020}
Insula, urges \citep{Jackson_2020}
Seed-based fcMRI in TS \citep{32065948}
Structural and functional network studies of "rage attacks" in TS \citep{Atkinson_Clement_2020}
Interestingly and intriguingly, hippocampal volume measured at the onset of tics in 41 children with provisional tic disorder predicted tic severity at one-year follow-up, with with a larger hippocampus at baseline predicting worse tic severity at follow-up \citep{jcm9061715}.
Pharmacological studies
Very cool CSF study on endocannabinoids \citep{32272483}
Anti-D2R autoantibodies in TS? \citep*{32662071}
Clinical and neuropsychological studies
Impaired associative learning in TS \citep{32544176}
Other
A direct pathway from somatosensory cortex influencing movement
Treatment
Psychological interventions
Behavior therapy (BT) is considered to be the first line treatment since publication of the 2019 AAN guidelines, based on controlled randomized trials. In a naturalistic setting (children and adolescents with chronic tics, n=74) and over a 12 month follow-up period, it could be demonstrated that BT is and remains effective in 75% of patients analyzed, attesting not only to its efficacy but durability \citep{Andrén2021}.
Internet-based BT programs are investigated by multiple groups to make BT available to a larger number of patients, rendering it thus independent on the availability of trained practitioners and financial considerations in countries where psychotherapy is not reimbursed by social security. Rachamin et al. offer preliminary data on internet-based guided self-help comprehensive behavioral intervention for tics (ICBIT) in 25 youths (passive control group/waiting list, n=16), and show this approach to be both effective and well received over a 6 month period. Larger trials including an active control group are necessary to confirm these first positive impressions \citep{Rachamim2020}.
Another way to increase access to BT for tic treatment is group training. The "Tackle your tics" program is an intensive four day course based on an enhanced version of ERP (exposure and response prevention). First results in 13 youth offer promising results regarding tic reduction and increased quality of life, with a tow month follow-up period. Larger controlled trials with longer follow-up periods are awaited awaited \citep{RN10144a}.
Still another approach is to train parents as therapists. For that purpose, an instructional video guide (on DVD) based on habit reversal training was developed and applied (n=33), and compared to in-person training (n=11) in children (mean age 10 years). Home-based, parent-administered HRT was as efficacious for tic reduction as traditional in-person training. However, the drop out rate in the former group was close to 50%, so that the authors advocate regular phone contacts during the DVD treatment course, which squares with other hybrid formats such at BipTic \citep{Singer2020}.
A very small (n=3) case series on an interesting new BT technique based on attention training to suppress tics: to be followed \citep{Schaich2020}.
So far, BT is usually proposed for children above the age of ten. In this very interesting proof of concept study, Bennett et al. test a CBIT format for children ages 5-8 (n=16) and show good response (tic reduction) and acceptance. Moreover, they monitor these improvements over a one year period and speculate that early BT might alter the chronic course of tics: this is a very important subject and should be investigated in larger, longitudinal cohorts \citep{Bennett2020}.
Medication
"Discontinuing ADHD medication may decrease quality of life for children" \citep*{laurel}\citep{32237294}
Neurosurgery
One site's long-term experience with DBS for OCD \citep{32184741}
Italian center's experience with antGPi vs. Cm-Pf DBS for TS \citep{32429219}
Structural connectivity predicts clinical DBS outcomes in TS \citep{32653920}