Davide Martino, PhD
National Parkinson Foundation International Centre of Excellence, Department of Neurology, King´s College Hospital, Denmark Hill, London, UK
Dystonia is regarded as a disorder of movement
According to the most recent classification issued last year by the Movement Disorders Society, dystonia is “a movement disorder characterized by sustained or intermittent muscle contractions”. Moreover, dystonia is worsened or even triggered by voluntary actions and may often interfere with voluntary movements, particularly when these require a high degree of precision. It seems beyond doubt, therefore, that dystonia is essentially regarded as a disorder of movement.
Recently more attention has also been paid to “non-motor” symptoms of dystonia
During the last 40 years, the most common forms of dystonia have been considered as conditions in which there was not much else to observe other than abnormal movements and postures. Recent studies, however, have raised attention on the occurrence of non-motor manifestations in primary dystonia, mainly involving sensations, emotions, cognitive functions, and sleep pattern. This should not appear excessively surprising if we think that the brain networks that generate dystonic movements and postures (such as those linking the cortex, basal ganglia and thalamus) may control a other functions including the processing of sensations, cognitive functions, emotions, and even of the sleep-wake cycle.
Neck dystonia and pain
Cervical (neck) dystonia is often associated with a discomfort in the neck region that may precede by weeks or months the first abnormal head movements. Later on in the course of the illness, patients with cervical dystonia experience pain in up to 75% of cases. The presence of pain is associated with greater severity of dystonia, worse quality of life and greater disability, and often leads to the need of targeting a higher number of muscles with botulinum toxin injections. The mechanisms of pain in cervical dystonia are still incompletely understood, and may involve muscular tension, deterioration of the cervical spine, and abnormal central sensitization to pain. Moreover, pain is currently investigated as one of the main targets of new physiotherapy approaches in this condition, and may respond also to deep brain stimulation surgery.
Other sensory impacts of dystonia
Among our patients with cervical dystonia followed up at King’s College Hospital, one third reports also numbness, tingling or pins and needles. Other sensory symptoms have been reported in other focal dystonias. Patients with blepharospasm are used to suffer from discomforting sensations such as dry or ‘sandy’ eyes and excessive sensitivity to light. There is some evidence that these symptoms might be due to ocular illnesses associated with blepharospasm, like dry eye syndrome, keratoconjunctivitis, or blepharitis, but this aspect remains still not completely defined. Albeit less commonly, irritation of the throat is also reported by patients with spasmodic dysphonia. The presence of these abnormal sensations supports the view that sensory stimuli in dystonia are processed differently than in the general population, and this might contribute to the overflow of muscle activity that is seen in this condition. It has been shown that the brain representation of the different body areas in patients with dystonia is different not only in the motor cortex, but also in the sensory cortex. In addition, the ability to perceive two touch stimuli applied one after the other as separate is less accurate in both patients with dystonia and in a proportion of their siblings without dystonia, suggesting that this sensory abnormality could be a trait of a genetic predisposition to dystonia. Finally, improved knowledge on the sensory features of dystonia might help exploring the potential efficacy of sensory input manipulation (including sensory training) as treatment strategy.
Impact of dystonia on the emotions
Primary dystonia has been documented to have an impact on the emotions. The frequency of a co-existing depressive disorder is higher in patients with cranio-cervical, laryngeal and focal hand dystonia in comparison to healthy people and other medical conditions. In our patients with cervical dystonia, more than 60% report loss of self-confidence. This may result from the stigma of visible torticollis, and may be associated with fear of certain social situations (social phobia), which has been documented as 10 times more frequent in cervical dystonia than in the general population. We also observed in our patients with cervical dystonia that at least one third of them reported feeling sad or depressed, or feeling nervous, worried or frightened for no apparent reason, with one in four highlighting flat moods without the normal “highs” and “lows”. Others have reported a diagnosis of mental health problems in up to 55% of patients with cervical dystonia, with depression and anxiety disorders being the most common. Depression and anxiety are not uncommon also in other focal dystonias, particularly in blepharospasm.
Dystonia and sleep
Increasing evidence supports that patients with primary dystonia, especially those with cervical dystonia, have a reduced quality of sleep, which is independent from pharmacological treatment or from the association with depression or anxiety. This observation comes from data obtained through validated questionnaires administered to patients, but not from more sophisticated sleep studies. Early studies in patients with blepharospasm and oromandibular dystonia who underwent polysomnography, the combined recording of brain, muscle, heart and respiratory activity during a night sleep, found impaired sleep efficiency, with reduced duration of deep sleep phases, including REM sleep whereas patients with primary generalised dystonia exhibited a more fragmented sleep with increased awakenings. There is clear evidence showing that sleep problems have an important effect on health-related quality of life in patients with cervical dystonia. This preliminary clinical evidence suggests that sleep is an important non-motor domain in primary dystonia, which deserves to be explored in greater detail. In addition, other subjective symptoms like the perception of fatigue, reported by almost half of patients with focal dystonias, might be aggravated by sleep problems and lowered mood.
Investigation of non-motor symptoms
To date, the investigation of non-motor symptoms in dystonia has been limited by the lack of a clinical instrument capable of screening the cumulative burden of these symptoms in a rapid and reliable fashion. Using the same approach in Parkinson’s, prof. K.R. Chaudhuri and other members of our team at King’s College Hospital have developed the Nonmotor Symptoms Questionnaire, currently recommended by several influential clinical guidelines worldwide, including the NHS NICE guidelines for Parkinson’s. We have recently developed a similar screening questionnaire for dystonia, the Dystonia Non Motor Symptoms Questionnaire (DNMS Quest), which comprises 14 yes/no questions that focus on the whole non-motor spectrum of symptoms in primary dystonia. In an exploratory survey, we assessed whether this questionnaire could be easily understood and completed by 102 patients with focal cervical dystonia, selected consecutively from our botulinum toxin outpatient clinic at King’s College Hospital. In this survey, we observed that non-motor symptoms are reported by 95% of patients, and more than one-third of them reported at least seven different non-motor symptoms. Stigma with loss of self-confidence and secondary isolation (62%), sleep dysfunction (60%), fatigue (51%) and light-headedness or dizziness (47%) appear to be dominant issues that need additional support in these patients. As we found a weak but significant correlation between the number of non-motor symptoms and motor severity, it could be speculated that the amount of non-motor symptoms may be worse in patients with more severe dystonia.
We are only just beginning to understand the potential burden of non-motor manifestations in primary dystonia, but initial observations are revealing us that their spectrum could be broader than previously known. There is still, however, much work that needs to be done in order to understand how much these symptoms are consequence of the dystonic movements or postures, and how much these are instead caused by dysfunction in the brain networks that underlie also the motor aspects of dystonia. In order to progress in this area, we need to be able to gather as much clinical information on non-motor features as possible from the largest number of patients. There are currently no validated bedside questionnaires and rating scales to characterise and measure non-motor symptoms in patients with dystonia. A holistic questionnaire exclusively focusing on this would allow capturing non-motor symptoms easily both in clinic and in research settings (e.g. for high quality epidemiological studies and clinical trials), and would ultimately guide clinicians on what should be prioritised in treatment, and what treatments to use. We hope that the on-going validation of the Dystonia Non Motor Symptoms Questionnaire in different languages would represent a first step in this direction.