Multiple Sclerosis (MS) is a chronic, autoimmune condition affecting the Central Nervous System (CNS), including the brain, spinal cord, and optic nerves. The immune system attacks myelin, the protective sheath around nerve fibers, causing damage known as lesions or plaques. Tics are defined as sudden, rapid, repetitive, and non-rhythmic movements (motor tics) or sounds (vocalizations). These involuntary actions range from simple eye blinking to complex movements or phrases. This article explores the relationship between MS and the onset of a tic disorder.
The Relationship Between MS and Tics
Multiple Sclerosis is considered a rare cause of primary tic disorders, which typically begin in childhood. The pathology of MS involves demyelination and inflammation predominantly within the CNS white matter. This white matter damage disrupts the transmission of nerve signals throughout the brain and body.
Tic disorders, including Tourette syndrome, are primarily linked to dysfunction in the cortico-striato-pallido-thalamo-cortical (CSPTC) circuit. This circuit relies on the basal ganglia and deep gray matter structures, which control movement selection and inhibition. Although MS lesions can occasionally occur in deep gray matter structures, this is not the typical pattern of the disease.
A tic disorder appearing secondary to a medical condition like MS is often termed “Tourettism.” The association between MS and a true tic disorder is so infrequent that only a handful of case reports exist in medical literature. Tics are not a standard feature of MS progression, unlike other movement disturbances.
Other Movement Disorders in MS
Movement symptoms are common in MS, but they often manifest as conditions other than tics, leading to potential misdiagnosis. One prevalent issue is tremor, an involuntary, rhythmic shaking. In MS, this often presents as an intention tremor, where shaking becomes more pronounced during purposeful movement, such as reaching for a cup.
Spasticity is another common motor symptom, characterized by muscle stiffness and painful spasms caused by increased muscle tone. This sustained muscle contraction is distinct from the sudden, brief, and non-rhythmic nature of a tic. Spasticity can interfere with walking and cause tightness, particularly in the legs.
Ataxia, a lack of muscle coordination, also frequently affects people with MS. Ataxia results in clumsy, unsteady movements, often related to lesions in the cerebellum or brainstem. These movements are characterized by poor balance and difficulty with precise motor control, separating them from the quick urges that precede a tic.
Potential Underlying Causes of Tics in MS Patients
If a person with MS experiences tics, the cause is usually secondary to the disease process or a co-occurring factor, not a typical MS symptom. One significant consideration is the potential for pharmacological causes, as tics can be a side effect of certain medications. Treatments prescribed for MS symptoms or co-morbid conditions, such as anticonvulsants or stimulants for fatigue, may affect neurochemistry and potentially trigger or worsen tics.
Psychological conditions frequently co-occur with MS and can play a role. Stress, anxiety, and depression are common, and these emotional states are known to increase the frequency and severity of pre-existing tics. Managing underlying anxiety or stress can sometimes reduce tic activity.
In rare instances where MS is directly implicated, case reports suggest an atypical lesion location is responsible. Lesions in deep brain structures, such as the basal ganglia or thalamus, or those affecting connecting white matter tracts, are necessary to disrupt the CSPTC circuit associated with tics. This direct causal link is extremely rare and involves a secondary tic disorder called Tourettism.
Diagnosis and Management of Tic Disorders
Accurate diagnosis is crucial, as tics can be confused with other MS-related movements like myoclonus or tonic spasms. A neurologist specializing in movement disorders performs a detailed neurological examination and often uses video analysis to characterize the movements as sudden, non-rhythmic tics. Tics are often preceded by a premonitory urge, a distinct physical sensation felt before the movement, which is a key diagnostic clue absent in most other MS movements.
Once confirmed, management typically begins with non-pharmacological interventions. Comprehensive Behavioral Intervention for Tics (CBIT) is the first-line treatment recommended by neurological guidelines. CBIT is a specialized behavioral therapy that teaches patients awareness of the premonitory urge and how to perform a competing voluntary movement to make the tic impossible to execute.
Pharmacological interventions are reserved for tics that are severe, distressing, or causing physical impairment. Medications often include alpha-2 adrenergic agonists, such as clonidine or guanfacine, which are considered first-line options due to their favorable side-effect profile. For severe cases, atypical antipsychotics like risperidone or aripiprazole may be used to suppress tic frequency and intensity.