Tremor is clinically defined by an involuntary rhythmic oscillatory movement of a body part. The most recent 2-axis classification scheme describes a clinical tremor syndrome in axis 1, mainly relying on tremor characteristics (body distribution, activation condition, tremor frequency, regularity, amplitude) and associated signs (isolated versus combined tremor syndromes). Based on further diagnostic tests (blood analysis, imaging, neurophysiology, genetic testing) the etiology is then described in axis 2, which may be acquired, genetic or idiopathic. The most common axis 1 isolated tremor syndromes are essential tremor and enhanced physiologic tremor, characterized by bilateral action tremor of the arms. Combined tremor syndromes relate to the accompanying neurologic sign or are described phenomenologically. These tremor syndromes relate to hyperoscillatory states of distinct networks, with the so-called cerebellar network playing a central role. Depending on the degree of disturbance as well as the additional involvement of other networks, specific tremor phenotypes emerge.

Tremor, which is defined as an oscillatory and rhythmic movement of a body part, is the most common movement disorder worldwide. The most frequent tremor syndromes are tremor in Parkinson’s disease, essential tremor, and dystonic tremor syndromes, whereas Holmes tremor, orthostatic tremor, and palatal tremor are less common in clinical practice. The pathophysiology of tremor consists of enhanced oscillatory activity in brain circuits, which are ofen modulated by tremor-related afferent signals from the periphery. The cerebello-thalamo-cortical circuit and the basal ganglia play a key role in most neurologic tremor disorders, but with different roles in each disorder. Here we review the pathophysiology of tremor, focusing both on neuronal mechanisms that promote oscillations (automaticity and synchrony) and circuit-level mechanisms that drive and maintain pathologic oscillations.

Tics are brief, sudden, movements (motor tics) or sounds (phonic tics) that are intermittent but may be repetitive and stereotypic (Jankovic et al., 2022). Although tics often spontaneously improve after childhood, they may persist into adulthood and become associated with a variety of comorbid disorders such as attention deficit disorder and obsessive–compulsive disorder. Tourette’s syndrome (TS), considered a genetic and neurodevelopmental disorder, is the most common cause of chronic tics. Motor and phonic tics consist of either simple or complex movements that may be seemingly goal directed. Motor tics may be rapid (clonic) or more prolonged. Many patients exhibit suggestibility and may have a compulsive component, sometimes perceived as an “urge” or a need to perform the movement or sound repetitively until it feels “just right.” Although tics are often considered relatively benign, many patients with TS have severe or disabling tics. “Whiplash” tics can produce disabling compressive myelopathy, and therefore need to be treated early and aggressively. When oral medications fail to provide satisfactory relief of tics, local chemodenervation with botulinum toxin (BoNT) offers the possibility of relaxing the muscles involved in focal tics without causing undesirable systemic side effects.

Tremor is one of the common movement disorders encountered by neurologists in clinical practice. Based on the history and phenomenology, the tremor can be classified commonly as Parkinson’s disease tremor, essential tremor , essential tremor plus, dystonic tremor, task-specific tremor and other tremor syndromes. This chapter describes the role of botulinum neurotoxin (BoNT) in several tremor conditions and provides some practical clinical pearls related to BoNT injection techniques. Specific muscles involved and the dose range of BoNT are tabulated.