MATERIALS & METHODS

We studied the video recordings and clinical charts of 201 consecutive patients with TS assessed within a 3-year period at Baylor College of Medicine. We enrolled patients fulfilling the diagnostic criteria of TS, chronic (persistent) motor/vocal tic disorder and provisional tic disorder according to the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) [6]. The presence of two or more motor tics and one vocal tic is required for a diagnosis of TS. For chronic (persistent) motor/vocal tics disorder, patients should present one or more motor or vocal tics, respectively, but not both. Tics should occur many times a day nearly every day for more than a year and start before age 18 in all cases [6]. For provisional tic disorder, symptoms should not last longer than 12 months. Patients with a tic disorder secondary to medications, drugs or other medical conditions were excluded [6].

For the purpose of this research, we divided blocking phenomena into two types, motor and phonic blocking phenomena, defined as partial or complete arrest in voluntary motor activity due to tic interference or a sustained and prolonged posture. We prefer the term “phonic” tic rather than “vocal” tic, as the former includes noises produced by the oro-facial-lingual apparatus rather than just the vocal cords [7]. Thus, phonic tics include noises such as sniffing or sounds produced with the tongue or teeth that would not be considered “vocal” tics. The number of different phonic tics was counted by the information obtained in clinical history and during analysis of video recordings.

Tic severity was assessed in each patient through the evaluation of video recordings. Severity was classified into six categories based on the Global Severity Rating and Rush Video-Based Tic Rating Scale [8,9]: 0: none; 1: very mild (tics rarely observed on video); 2: mild (tics are noticeable but not disruptive); 3: medium (tics are frequent but mildly disruptive); 4: marked (tics are severe and disruptive); 5: severe (tics are very severe and disruptive); 6: very severe (tics are extremely disruptive). We also assessed the severity of tics by clinical history, according to what was reported by the patient or a close family member. We recognized three categories: 1) mild: tics were focalized or infrequent, causing minor or no disruption in daily living activities or at work or school; 2) moderate: tics were frequent and extensively distributed, causing some disruption in daily living activities or at work or school; and 3) severe: tics were frequent, causing severe disruption in daily living activities or at work or school.

We assessed the frequency of comorbid OCD or behavior and attention-deficit/hyperactivity disorder according to the DSM-5 criteria [6]. Patients or a close family member provided written signed informed consent, approved by the Baylor College of Medicine Institutional Review Board for Human Research for videotaping and publication in a scientific journal.

Statistics

We summarized data as percentages and means and standard deviations. The odds ratio (OR) with 95% confidence interval (C.I.), chi-square test or Fisher’s exact test were performed to compare risks and proportions between groups. The t test for independent samples was used to compare means between patients with and without blocking phenomena. Statistically significant variables (p < 0.05) obtained in the bivariate analysis were included in a backward stepwise conditional Wald method for multivariate logistic regression, with the presence or absence of blocking phenomena as the dependent variable. The exponentiation of B (ExpB) coefficient was used to provide an estimated weight of the independent variable. Variables with a p value > 0.10 were eliminated from the final equation. Statistical interactions between significant independent variables were assessed in the general multivariate model. The Hosmer‒Lemeshow test was used to assess the goodness of fit for the final regression model, and a p value < 0.05 was considered poor fit. All statistical evaluations were carried out with SPSS version 22 (IBM Corp., Armonk, NY, USA); we considered a p value < 0.05 to be significant.

RESULTS

We identified 12 patients (11 males) with blocking phenomena, representing 6% of the total cohort. There were 8 (4%) patients with phonic blocking phenomena, characterized by interference of normal speech by tics (Supplementary Videos 1 and 2 in the online-only Data Supplement), and 4 (2%) patients with motor blocking phenomena, characterized by synchronous extensive muscle contractions involving the limb, trunk and craniocervical muscles (Supplementary Videos 3 and 4 in the online-only Data Supplement).

There was a statistically significant association between the presence of blocking phenomena and shoulder tics (OR: 3.96, C.I. 95%: 1.04–15.1; p = 0.031), leg tics (OR: 4.23, C.I. 95%: 1.3–13.9; p = 0.018), copropraxia (OR: 8.6, C.I. 95%: 1.9–39.2; p = 0.016), dystonic tics (OR: 3.72, C.I. 95%: 1.14–12.18; p = 0.032), simple phonic tics (OR: 1.09, C.I. 95%: 1.04–1.14; p = 0.021), number of phonic tics per patient (p = 0.002), and diagnostic criteria of TS (OR: 1.09, C.I. 95%: 1.04–1.14; p = 0.039). However, a statistical trend was observed for arm tics, complex motor tics, tonic tics, coprolalia, OCD and diagnostic criteria for persistent (chronic) motor tic disorder in the bivariate analysis (Table 1). In the stepwise multivariate logistic regression, dystonic tics (p = 0.012) and a higher number of phonic tics (p = 0.022) were statistically related to the presence of blocking phenomena (Table 2).

DISCUSSION

Blocking phenomena in TS are characterized by a transient cessation of motor activity. We found a 6% prevalence of blocking phenomena among 201 patients with TS. This figure is relatively small compared to the 37.4% frequency among 195 patients with TS reported by Kaczyńska and Janik [5]. In the latter study, the most frequent blocking phenomenon was the cessation of walking (80.8%), followed by speech arrests (26.0%). The difference in the frequency of blocking phenomena between that study and ours may be explained by the different methodologies employed in both studies. In our study, we documented blocking phenomena during an in-person examination and video recording, while the other study relied on recollection of blocking tics in the course of their TS as ascertained by a structured interview. The relatively low prevalence of blocking tics encountered in our study is more in accordance with data reported by Ganos et al. [3] These authors included only blocking phenomena related to tics, similar to our study, whereas the study by Kaczyńska and Janik [5] may have included blocking phenomena related to other etiologies. Pure negative phenomena were not assessed in our study, as negative phenomena are nonspecific and can be related to OCD, anxiety, panic attacks, posttraumatic stress disorder, functional (psychogenic) phenomena, etc., rather than a tic. The blocking phenomena in our patient also manifested during walking. Similar to speech arrests, this phenomenon may result from a brief tonic contraction of axial and limb or trunk muscles (analogous to dystonic tics) or due to interruption of or inability to access ongoing motor programs.

In our study, we classified blocking phenomena as motor and phonic. We found that patients with motor blocking phenomena had prolonged tics causing arrests or blockage of voluntary muscle activity; patients with phonic blocking phenomena had speech arrests mainly due to intrusions of tics, blocking the normal fluency of speech.

The blocking phenomenon during speech has been highlighted in the medical literature in single case reports. The speech of such patients is described as a stuttering-like dysfluency caused by “blocking tics” and palilalia [10]. This speech pattern resembles “cluttering”, which is defined as transient breaks in speech with voiceless pauses [11,12]. Patients with TS seem to have more speech dysfluencies than normal controls [13,14]. It is possible that at least some of that dysfluency is related to blocking phenomena. Isometric contractions of the abdominal or respiratory muscles producing a Valsalva maneuver may underlie blocking tics [1].

We found a statistically significant association with the presence and higher number of phonic tics, suggesting that the presence of simple phonic tics increases the risk of phonic blocking phenomena in patients with TS. Interestingly, complex phonic (or vocal) tics were not related to blocking phenomena in the multivariate regression, perhaps because they require more elaborate motor programs, making them less susceptible to speech interference.

Some of our patients exhibited motor blocking phenomena related to tonic (sustained isometric muscle contractions) or dystonic (prolonged agonist muscle contractions resulting in a sustained abnormal posture) [15]. We emphasize that the definition of blocking motor tics in our study required an inability for voluntary muscle activity. It is important to differentiate tonic and dystonic tics; the latter are defined as tics with more sustained isotonic muscle contractions usually lasting > 1,000 ms [15]. Tonic tics are sustained isometric muscle contractions, for example, intermittent platysma contractions. The bivariate analysis showed a statistically significant association with dystonic tics (p = 0.032), and a trend for a higher frequency of tonic tics favoring patients with motor blocking phenomena was also observed (p = 0.069). The multivariate analysis showed a significant association between blocking phenomena and the presence of dystonic tics (p = 0.014). This suggests that blocking tics represent an extreme form of dystonic and possibly tonic tics.

Although diagnostic criteria for TS and other motor phenomena, such as copropraxia and shoulder and leg tics, showed a relationship with blocking phenomena in the bivariate analysis, significance was lost after controlling for other variables. Although it may be argued that these patients have a form of functional (psychogenic) overlay, we did not find any evidence in support of this hypothesis, such as prominent suggestibility, distractibility, or periods of unexplained improvement or worsening [16].

Compulsion may also underlie motor blocking phenomena. In our study, a statistically significant trend for a higher frequency of OCD was observed in patients with motor blocking phenomena in the bivariate analysis (p = 0.054), but the trend was lost after controlling for other variables. Another study also found a statistical association with OCD in the bivariate analysis that was lost in the multivariate regression [5]. These data suggest that OCD may have an effect on the pathogenesis of blocking tics, but it is not necessary and probably not sufficient for causing blocking tics. However, larger studies should clarify whether there is a relationship between OCD and motor blocking phenomena.

We found an association between greater severity of tics by clinical history and video analysis and blocking phenomena and a statistically significant trend with complex motor tics. Similar findings were reported by Kaczyńska and Janik [5]. This suggests that blocking tics cluster in the highest spectrum of TS severity. The latter is supported by the higher number of motor tics found in that study [5] and the higher number of phonic tics found in our study.

As this cohort was studied in a tertiary referral center for TS, a selection bias is possible with the inclusion of severely affected patients. However, the entire spectrum of tic severity was detected in our patients, ranging from mild to severe. Although the number of patients with blocking phenomena was low in this study, the multivariate regression model showed a proper goodness of fit. We were not able to evaluate clinical groups separately due to the low number of cases. Further studies should address the impact of blocking phenomena on quality of life as well as response to behavioral, pharmacological and neuromodulation therapies such as deep brain stimulation.

In conclusion, blocking phenomena were observed in 6% of patients with TS in this study. Two basic phenomena are identified: phonic and motor blocking phenomena. They represent positive, intrusive or sustained motor phenomena and transitory arresting volitional motor activity. Negative phenomena (absence, suppression, or inhibition of motor activity) may also occur in patients with TS, but their pathophysiology may be variable and not necessarily related to tics. Further neurophysiological studies, including Bereitschaftspotential, transcranial magnetic stimulation, and functional magnetic resonance imaging, will be valuable to better elucidate the pathophysiologic basis of blocking phenomena.

Notes

Conflicts of Interest

The authors have no financial conflicts of interest.

Funding Statement

None

Author contributions

Conceptualization: José Fidel Baizabal-Carvallo, Joseph Jankovic. Data curation: José Fidel Baizabal-Carvallo. Formal analysis: José Fidel Baizabal-Carvallo. Investigation: José Fidel Baizabal-Carvallo. Methodology: José Fidel Baizabal-Carvallo. Resources: Joseph Jankovic. Supervision: Joseph Jankovic. Validation: Joseph Jankovic. Visualization: José Fidel Baizabal-Carvallo, Joseph Jankovic. Writing—original draft: José Fidel Baizabal-Carvallo. Writing—review & editing: José Fidel Baizabal-Carvallo, Joseph Jankovic.

Supplementary Material

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Figure & Data

References

Citations

Citations to this article as recorded by  

• Oromandibular tics associated with Tourette syndrome
  José Fidel Baizabal-Carvallo, Marlene Alonso-Juarez, Joseph Jankovic
  Journal of Neurology.2023; 270(5): 2591.     CrossRef

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