From the Guidelines
Cervical dystonia is characterized by abnormal brain signaling leading to involuntary muscle contractions in the neck, primarily due to dysfunction in the basal ganglia and alterations in neurotransmission. The pathophysiology of cervical dystonia involves complex mechanisms, including disrupted balance in the basal ganglia, particularly the putamen and globus pallidus, which normally regulate smooth movement through balanced inhibitory and excitatory pathways 1. This disruption leads to reduced inhibition and excessive muscle activation. Neurochemically, alterations in dopamine, GABA, and acetylcholine neurotransmission play a significant role. Additionally, sensory processing abnormalities contribute to the condition, with impaired integration of proprioceptive information from muscle spindles. Some key points to consider in the pathophysiology of cervical dystonia include:
- Dysfunction in the basal ganglia, affecting the regulation of movement
- Alterations in neurotransmission, including dopamine, GABA, and acetylcholine
- Sensory processing abnormalities, particularly in proprioceptive information integration
- Genetic factors, such as mutations in THAP1, GNAL, and ANO3, in some cases
- Neuroplasticity changes over time, with reorganization of sensorimotor cortical maps and altered intracortical inhibition The condition manifests as sustained or intermittent contractions of the sternocleidomastoid, trapezius, splenius, and other neck muscles, causing abnormal head postures. These pathophysiological mechanisms explain why treatments targeting neurotransmitter systems or directly reducing muscle activity can be effective in managing symptoms, as noted in guidelines on the uses of botulinum neurotoxin for treating cervical dystonia 1.
From the Research
Pathophysiology of Cervical Dystonia
The pathophysiology of cervical dystonia (CD) is complex and not fully understood. However, several studies have shed light on the underlying mechanisms:
- Cervical dystonia is characterized by involuntary, abnormal movements and postures of the head and neck, resulting from sustained involuntary muscle contractions 2.
- The disorder is thought to involve faulty sensorimotor integration and impaired motor planning, similar to focal hand dystonia 3.
- Functional brain connectivity studies have revealed altered connectivity in various neural networks, including the sensorimotor network, primary visual network, and executive control network 3.
- The trigeminal sensory nuclear complex (TSNC) may play a central role in the pathophysiology of craniocervical dystonia, including CD, by mediating aberrant reflexes and disordered sensorimotor control 4.
Neural Networks Involved
Several neural networks are involved in the pathophysiology of CD:
- The sensorimotor network, which comprises the premotor cortex, supplementary motor area, primary sensorimotor cortex, and secondary somatosensory cortex, shows reduced connectivity in CD patients 3.
- The primary visual network, which originates from the occipital cortex, also shows reduced connectivity in selected regions 3.
- The executive control network, which includes the prefrontal cortex and parietal cortex, shows increased connectivity, possibly as a compensatory mechanism 3.
Clinical Features
CD can present with a range of clinical features, including:
- Abnormal postures and movements of the head and neck, such as rotation, flexion, extension, and tilt 2.
- Pain, local muscle hypertrophy, and abnormal EMG activity 2, 5.
- Sensory tricks, such as touching the chin or back of the head, can temporarily ameliorate dystonic movements and postures 2.
- Some patients may experience symptoms without abnormal movements, such as pain or local muscle hypertrophy, which can be considered a pro-dromal or formes fruste form of CD 5.