Chorea and Basal Ganglia Dysfunction

Pathophysiology of Chorea

Chorea is characterized by involuntary, flowing, non-stereotyped movements that often possess a writhing quality, resulting from dysfunctional neuronal networks interconnecting the basal ganglia and frontal cortical motor areas 1
The most common focal MRI abnormality in choreiform disorders involves the basal ganglia (60%), predominantly affecting the anterior caudate and putamen 1, 2
The abnormal basal ganglia-thalamo-cortical circuit is considered the pathophysiological basis for many movement disorders including chorea 3

Huntington's disease (HD) is the prototypical choreiform disorder and most common cause of chorea in adults 1
In HD, abnormal aggregates of the huntingtin protein accumulate in the brain, leading to the loss of GABAergic medium spiny neurons, particularly in the striatum 1
Progressive and disproportionate volume loss of the neostriatum is a hallmark finding on imaging studies in HD 1

In Wilson's disease, structural abnormalities in the basal ganglia are frequently detected on neuroimaging 4, 5
Simultaneous involvement of basal ganglia, thalamus, and brainstem (found in 55.3% of cases) is highly specific for Wilson's disease 4, 5

Multiple sclerosis (MS) can cause secondary paroxysmal kinesigenic dyskinesia (PKD) when lesions involve the thalamus, lenticular nucleus, globus pallidus, and internal capsule 3
Calcification of the basal ganglia, including idiopathic basal ganglial calcification and calcification secondary to hypoparathyroidism or pseudo-parathyroidism, may cause secondary chorea 3

MRI is the optimal imaging modality for evaluating chorea, with the most sensitive sequences being diffusion-weighted and T2-fluid-attenuated inversion recovery (FLAIR) 1, 2
Functional MRI studies have revealed abnormal connectivity between the thalamus and motor cortex in patients with movement disorders 3
In patients with PRRT2 mutations (causing paroxysmal kinesigenic dyskinesia), thalamo-prefrontal hypoconnectivity has been observed, indicating inefficient thalamo-prefrontal integration and dysfunction of motor inhibition 3

Genetic testing is the diagnostic test of choice for suspected Huntington's disease and should be performed in concert with initial imaging 1
In cases of suspected Wilson's disease, MRI should be considered prior to treatment in all patients with neurologic manifestations 4, 5