Basal ganglia motor function in relation to Hallervorden-Spatz syndrome

Current and emerging strategies for treatment of childhood dystonia

Childhood dystonia is a movement disorder characterized by involuntary sustained or intermittent muscle contractions causing twisting and repetitive movements, abnormal postures, or both (Sanger et al, 2003). Dystonia is a devastating neurological condition that prevents the acquisition of normal motor skills during critical periods of development in children. Moreover, it is particularly debilitating in children when dystonia affects the upper extremities such that learning and consolidation of common daily motor actions are impeded. Thus, the treatment and rehabilitation of dystonia is a challenge that continuously requires exploration of novel interventions. This review will initially describe the underlying neurophysiological mechanisms of the motor impairments found in childhood dystonia followed by the clinical measurement tools that are available to document the presence and severity of symptoms. Finally, we will discuss the state-of-the-art of therapeutic options for childhood dystonia, with particular emphasis on emergent and innovative strategies.

Pallidal stimulation for dystonia in pantothenate kinase-associated neurodegeneration

Patients with generalized dystonia secondary to pantothenate kinase-associated neurodegeneration are traditionally treated palliatively with medical therapy. Therapeutic advances include stereotactic basal ganglia ablative techniques and, more recently, pallidal deep-brain stimulation. We report the course of dystonia in a teenage male. Bilateral microelectrode-guided pallidal deep-brain stimulators were placed while the patient was awake. Three parasagittal microelectrodes were inserted simultaneously. Two anterior microelectrodes were relatively quiet. The posterior electrode demonstrated a pattern of frequent bursts with high-frequency activity. The stimulator was therefore placed in the posterior location, which resulted in symptomatic improvement. Pallidal deep-brain stimulation appears to create a functional correction that may alter globus pallidus internus inhibitory output to the motor thalamus. The prominent, noisy bursting patterns observed in the globus pallidus internus suggests that high-frequency stimulation may improve signs of dystonia by normalizing thalamic discharge patterns.

Identification of axonal involvement in Hallervorden-Spatz disease with magnetic resonance spectroscopy

Hallervorden-Spatz disease is a neurodegenerative disorder associated with cysteine-iron complex accumulation typically seen as bilateral symmetrical hypointense signal changes in the medial globus pallidus on magnetic resonance imaging. We used magnetic resonance spectroscopy to identify and quantify neuronal damage in two siblings with Hallervorden-Spatz disease. The first patient presenting with a rapidly progressive extrapyramidal syndrome had markedly decreased N-acetylaspartate (NAA) to creatinine (Cr) ratios in the globus pallidi and the periatrial white matter. He also had increased myoinositol (mI) to creatinine (Cr) ratios implying glial proliferation in the affected regions. However the second patient who had the initial presentation of disease had normal NAA/Cr and mI/Cr ratios. These findings indicate that the quantification of NAA:Cr and mI:Cr ratios might be used to predict the extent of neuronal axonal loss and glial proliferation in patients with Hallervorden-Spatz disease respectively.

Reaching movements in childhood dystonia contain signal-dependent noise

When reaching, children with dystonia exhibit movements that are slower and more variable than normal children. We hypothesize that in dystonia there is an increase in signal-dependent noise so that there is increased variability with increasing speed. This hypothesis predicts that slower movement in children with dystonia is at least partly due to a compensatory strategy to reduce variability by decreasing speed. To test this hypothesis, we measured the speed of arm movement while children attempted to contact buttons of different sizes. We tested 23 control children and 15 children between the ages of 4 and 16 years with dystonia owing to either cerebral palsy, idiopathic dystonia not due to the DYT1 (torsin A) mutation, or other identified causes. A consistent inverse relationship between movement time and button size was seen for both the control children and the children with dystonia. The variance of movement speed increased with the average speed for all subjects. Children with dystonia moved significantly more slowly at all button sizes, and their movement speed was more sensitive to changes in button size. Therefore, part of the reduction in speed in dystonia is due to relatively greater difficulty in contacting small targets. This finding is consistent with the hypothesis of increased signal-dependent noise in children with dystonia, and we present a simple computational model that provides a possible explanation for the origin of this noise.

Progressive dystonia in a 12-year-old boy

Pantothenate kinase-associated neurodegeneration (PKAN) (MIM 234200; Hallervorden-Spatz syndrome) is a degenerative, autosomal recessive disorder in childhood, currently without specific treatment. In contrast to variable clinical features, T2-weighted magnetic resonance images show a characteristic 'eye-of-the-tiger sign' in the globus pallidus due to excess iron deposition. Recently a defect in pantothenate kinase, the key regulatory enzyme in the synthesis of coenzyme A from pantothenate, has been identified as the cause of the disease. We report a 12-year-old boy with progressive rigidity, dystonia, impaired voluntary movement, dysarthria, and mental deterioration. Over 10 years the boy had been misdiagnosed with clumsiness, emotional and behavioural deficits, and attention deficit disorder, before neuroimaging was performed showing the characteristic 'eye-of-the-tiger sign'. Molecular analyses confirmed two mutations in the PANK2 gene [coding sequence of a gene that has homology to murine pantothenate kinase-1]. We conclude that in progressive childhood dystonia, PKAN should be considered and magnetic resonance imaging performed early. The newly described defect of the pantothenate kinase enzyme enables a novel therapeutic approach to be considered, based on the mutation analyses of the PANK2 gene, as well as the prenatal diagnosis of this disorder.