From the Guidelines
Focal movements are caused by abnormal excessive or synchronous neuronal activity in a single cerebral hemisphere.
Causes of Focal Movements
- Abnormalities in brain structure, such as tumors, infections, infarctions, traumatic brain injuries, vascular malformations, and developmental abnormalities 1
- Genetic defects, such as those seen in malformations of cortical development (MCD) 1
- Neurological conditions, such as epilepsy, which can be caused by various factors, including infections, trauma, poisonings, lack of oxygen, and metabolic abnormalities 1
Characteristics of Focal Seizures
- Arise within networks of a single cerebral hemisphere and may remain localized or become more widely distributed 1
- Can be further characterized by having motor onset or nonmotor onset symptoms and can also be characterized by being aware or having impaired awareness 1
- Can present as jerking of only one extremity or one side of the body, abnormal facial movements, small repetitive movements, or staring spells (focal impaired awareness), with or without changes in consciousness 1
From the Research
Causes of Focal Movements
The exact causes of focal dystonia have yet to be determined, but several possible causative factors have been identified at all levels along the sensorimotor pathway, including:
- Anatomical constraints of the hand (musicians) 2
- Abnormal co-contractions of the muscles due to reciprocal inhibition in the spinal cord 2
- Subcortical and cortical remapping 2
- Deficiencies in sensorimotor integration and perceptual deficits 2
- Cerebellar involvement in the network and mechanisms underlying sensory abnormalities 3
Risk Factors for Focal Dystonia
Certain risk factors have been identified for the development of task-specific focal dystonia, including:
- Number of practice hours 2
- Personality 2
- Genetic predisposition 2
- Performance factors 2
- Sensory effects 2
Pathophysiology of Focal Dystonias
The traditional hypothesis that the pathophysiology of focal dystonia entails a single structural dysfunction (i.e. basal ganglia) has recently come under scrutiny, and a network disorder model has been proposed, implying that focal dystonias arise from aberrant communication between various brain areas 3. Additionally, nonmotor disturbances, including sensory processing abnormalities, have been reported to be associated with focal dystonias 3.
Differential Diagnosis
It is also important to differentiate focal dystonias from other conditions, such as epilepsy, as dystonic posturing could be one of the accompanying features of epilepsy 4.