Dystonia

INDEX

Three important aspects of dystonia should be highlighted before delineating the details of the clinical examination:

  1. Abnormal Physiology

With respect to examination findings, it is appropriate to highlight two areas of abnormal physiology found in dystonia; both are likely to depend on an inbalance between excitatory and inhibitory circuits because of defective inhibitory mechanisms operating at various levels of the central nervous system16:

  • The presence of sustained simultaneous co-contraction of agonist and antagonist muscles (which can be triggered or worsened by task-specific actions and relieved by some sensory tricks)
  • An excess of movement with loss of selectivity, and with involvement of adjacent or distant muscles (“overflow”).

 

  1. Variability of Phasic Dystonic Movements

An important clinical feature of dystonia, which makes for a challenging differential diagnosis with other movement disorders, is the variable speed of phasic dystonic movements.  These features have to be looked for in all movement disorders, either fast or slow, especially when the immediate impression is that of a tremor, tic, chorea, or myoclonus. Phasic dystonic movements include:

  • Rapid and jerky movements, resembling myoclonus or tics
  • Slow (athetoid dystonia) movements.
  • Rhythmic (dystonic tremor). 

 

  1. Progression of dystonia with time19:
  • Dystonic movements are frequently worsened during voluntary movement (action dystonia), and idiopathic dystonia commonly begins with a specific action, ie action dystonia. 
  • In some cases, as the dystonic condition progresses, less specific action of the leg affected by dystonia may activate dystonia (e.g. when tapping the floor).
  • With further evolution of underlying dystonia, action in other parts of the body can induce dystonic movements of the involved leg, a state referred to as overflow.
  • With further deterioration, dystonia may be present even at rest. Eventually the limb may go into sustained posturing.

 

 

Figure illustrates the distinct clinical features of dystonia.

From: Martino D, Espay AJ, Fasano A, Morgante F. Disorders of Movement: A Guide to Diagnosis and Treatment. Berlin-Heidelberg: Springer; 2016 6.

 

Phenomenological features of dystonia.

  1. Dystonia is related to voluntary movement:
  • Dystonia and dystonic postures are often triggered or worsened by attempts at voluntary movement or posture, and are associated with the phenomenon of overflow.
  • Movements are often sustained at their peak, and dystonic movements often resemble a spasm.
  • The presence of abnormal postures that are superimposed upon, or substitute for voluntary movements, is a characteristic feature of dystonia20.
  • Dystonia is typically influenced by voluntarily maintained posture, as in antigravity support.
  • At an extreme of its relationship to voluntary movement, dystonia may only be present with specific voluntary actions.

 

  1. Dystonia is position sensitive:
  • Consequently it is important to examine for features of dystonia by careful inspection of the arms during posture holding and batwing positions (arms flexed at the elbows and the forearms pronated with the fingers held near the nose).
  • Dystonic features may be brought out by asking the patient to hold the arms extended in front of their body for 30–60 seconds. In this setting, dystonic thumb flexion and other dystonic postures may be seen.
  • In addition, the patient should slowly rotate the outstretched arms from pronation to supination, since this may show a position-specific tremor, indicating an underlying dystonic tremor.

 

  1. Presence of a null point:
  • Certain positions may be associated with lessening, or virtual disappearance of the dystonia or tremor, termed a null point. For example, when the body part is positioned in the maximum direction of the movement (eg turning the head to the right in right latero-collis)7.
  • Limbs may be passively positioned by the examiner in search for a “null point” as well. Common positions include extreme pronation, supination, flexion and extension of the wrists.
  • Lessening of movements or detecting a null point may be sought by asking the patients to adopt their preferred posture (usually opposite to the direction of movement).

 

  1. Dystonia has directionality:
  • After the maximum movement, it will tend to lessen gradually in a preferred posture (usually opposite to the direction of movement).
  • Dystonic movements are modulated by body segment position, which gives them directionality.
  • Usually, dystonic tremor increases in amplitude when moving away from the usual direction of the dystonic contractions, and tends to show much greater right–left asymmetry than ET.
  • In patients with dystonic tremor of the head, the head tends to be pulled in one direction and released back in the other direction, rather than for the head to rotate symmetrically around a central vertical axis. As the patient moves their head from right to left, there may be clear asymmetry of tremor.

 

  1. Dystonia is patterned and relatively stereotyped.  In children, foot inversion, wrist ulnar deviation, or lordotic trunk postures are particularly common20.
  • The movements usually have a patterned and repetitive nature, and are consistent and predictable since they involve the same group of muscles, as opposed to chorea, where movements are random.
  • The movement is predictable, as it involves one or more body regions.
  • Contractions have a consistent direction, or result in a consistent posture.
  • It should also be noted that there may be multiple dystonic postures in the same patient, so that different dystonic postures may be combined20.

 

  1. Dystonia involves specific locations. 
  • These regions may be involved individually (focal dystonias) or in different combinations (segmental, multifocal, or generalized dystonias). Body distribution may change over time, typically with progression to previously uninvolved sites
  • The upper or lower cranial region
  • The cervical region
  • The larynx
  • The trunk
  • The upper limbs
  • The lower limbs.

 

  1. Dystonia is associated with abnormal postures.
  • Muscle contractions may be continuous, forcing limbs and trunk into sustained postures but they may also be discontinuous and irregular.
  • A body part is flexed or twisted along its longitudinal axis. Slowness and clumsiness for skilled movements are associated with sensation of rigidity and traction in the affected part2.
  • Postural changes may be spasmodic or tonic, dynamic or fixed, or any combination.
  • Postures tend to occur at intervals determined by voluntary movement and can be sustained for variable lengths of time. Relaxation may be impaired so that the dystonic posture may be maintained well beyond the end of the attempted voluntary movement that triggered it20.
  • In spasticity, the severity of the abnormal posturing tends to be constant throughout the gait cycle, whereas dystonic posturing often varies. For example, in a dystonic gait, the ankle might be inverted during the early swing phase but then normalize or even become everted just before the stance phase5.
  • Dystonic stiffness and posturing of the legs can improve significantly or may even be absent during different walking tasks, such as walking backwards, walking heel to toe, or running, whereas a spastic gait does not change significantly according to task5.

 

  1. Dystonia is associated with phasic movements. Phasic dystonia can mimic many other movement disorders (eg tremor, tics).  In the case of obvious underlying abnormal posturing, the clue that the associated phasic movement is dystonic is that it occurs in the same part of the body5. However, if phasic dystonia dominates, then there may be only subtle, stereotyped, abnormal posturing in the body part(s) affected by the involuntary movements that provides the clue to its dystonic origin. The patient needs to be instructed to allow the involuntary movement to occur freely, because voluntary compensatory postures or movements can be misleading. For example, a latent abnormal posture underlying tremor-dominant cervical dystonia often can be revealed by asking the patient to relax with eyes closed and let the head drift where it feels most comfortable, revealing underlying torticollis or other dystonia.  These phasic movements may appear to be:
  • Rapid and jerky, resembling myoclonus or tics
  • Slow (athetoid dystonia)
  • Rhythmic (dystonic tremor).
    • The dystonic tremor may not be relieved by allowing the abnormal dystonic posture to fully develop without resistance (“null point”).
    • Dystonic tremor may be difficult to distinguish from essential-type tremor.
    • Dystonic tremor is often more irregular in timing and amplitude than non-dystonic tremor, since the underlying muscle bursts are irregular in duration and amplitude. 

 

  1. Dystonia may have abnormalities in tone.
  • In dystonia, resting hypertonia is relatively uncommon and, when present, tends to be variable20.
  • Some patients with task specific dystonia may show additional increased tone, reduced arm swing and effortful repetitive movements in the involved limb but without decrement of the amplitude of the movement (bradykinesia).Gasser

 

  1. Dystonia is characterized by the presence of sensory tricks (Gestes antagonistes). 
  • Sensory tricks are voluntary actions performed by patients that reduce or abolish the abnormal posture or the dystonic movement, usually by simple light touch.  They are usually simple movements directed to, the body region affected by dystonia, and are not the exercise of force to overcome the dystonic movement.
  • Alleviation of dystonia occurs immediately and affects both tonic and phasic components.
  • Alleviation of dystonia occurs during the geste movement, usually soon after its start.
  • Alleviation of dystonia may last for as long as the geste lasts, or slowly reverse spontaneously before its end.

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Common gestes antagonistes: stretching out the arms in a patient with truncal dystonia.

From: Morgante F, Klein C. Dystonia. Continuum (Minneap Minn). 2013;19(5 Movement Disorders):1225-1241. doi:10.1212/01.CON.0000436154.08791.67 13.

 

  1. Dystonia is associated with Overflow: together with mirror dystonia, the presence of overflow may prove particularly helpful in cases of dystonia with mild or inconstant phenomenology.
  • Overflow refers to the spread of involuntary activity to an unaffected (usually contiguous but also contralateral) body part distinct from the primary site of dystonia7.  In terms of localization of dystonia, this is therefore a dystonic contraction, which arises in one body segment but may spread to another segment. It is usually ipsilateral, and may be seen by inspection, or recorded with EMG. This commonly occurs at the peak of dystonic movements.

 

  1. Dystonia is associated with Mirror dystonia:
  • Mirror dystonia is a unilateral posture or movement with the same or similar characteristics to the patient’s dystonia (usually dystonic postures and some movements) that can be elicited, usually in the more severely affected side, when contralateral movements or actions are performed by the homologous opposite, usually normal, body part.
  • Specific task(s) which can elicit mirror dystonia may need to be identified to elicit mirror dystonia.  A typical example, observed in almost half of the patients with writer’s cramp, is mirror dystonia of the dominant hand while writing with the opposite unaffected hand.
  • Ask the patient to perform repetitive hand tasks with each hand sequentially such as finger tapping, normal writing, or piano-like movements, rapid opening and closing of the hand, and hand pronation–supination; these should be performed at slow and fast speeds in the non-affected limb.
  1. Dystonia is associated with changes when writing
  • Ask the patient to write sentence repetitively. When evaluating the writing task, make sure shirt sleeves are pulled up. Ideally, the feet are exposed as well.
  • Ask the patient if (s) he feels tightness in the limb.
  • In an affected limb, look for tight grip of the pen, unusual posturing of the hand that may progress as the patient continues to write, and involvement of more proximal muscles.
  • Look for dystonic mirroring/overflow in another limb, and look for involuntary toe flexion, extension or foot inversion that would suggest dystonic overflow.