Objective: To describe the outcome of deep brain stimulation (DBS) to the globus pallidus interna (GPi) in an adult patient with idiopathic truncal dystonia with a rare extensor phenotype.

Background: Focal dystonia is the most common type of adult-onset dystonia, however, it infrequently affects truncal musculature.  Most patients with primary truncal dystonia exhibit flexion while truncal extension is rare and often attributed to secondary etiologies such as tardive syndromes and neurodegenerative disease.  However, adult-onset idiopathic truncal dystonia with primary extensor phenotype has been reported. The majority of these patients are refractory to oral medications and botulinum toxin injections.   Although the efficacy of DBS for primary dystonia, especially generalized DYT-1 positive dystonia, is well established; it has been shown to be efficacious for idiopathic truncal dystonia, specifically camptocormia, with no known reports of its application for an idiopathic focal extensor phenotype. 

Methods: We present a case of a 49 year-old woman with no known family history of dystonia who complained of backward pulling of her trunk.  At age 35, she developed abnormal arching of her back, which progressed to stereotyped extension and rightward tilting of her back that emerged when standing or walking.  The dystonia abated in the seated or supine position. This caused severe difficulties walking and she employed sensory tricks such as running or leaning against a wall.   She was not exposed to neuroleptics or antiemetics and had no structural lesions on her brain MRI. Trials of trihexyphenidyl, baclofen, carbidopa/levodopa, leviteracetam, hydroxyzine and botulinum toxin injections were not beneficial.

Results: Staged bilateral GPi DBS was implanted without complications. Improvement in the pre-operative Burke-Fahn-Marsden Dystonia Rating Scale motor score went from 12 to 4 at four months after initial programming and her disability score improved from 5 to 3.

Conclusions: GPi DBS can be particularly beneficial in patients with the rare phenotype of truncal extension in idiopathic truncal dystonia refractory to medications and botulinum toxin injections. 

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-case-of-idiopathic-adult-onset-truncal-extension-dystonia-treated-with-bilateral-pallidal-deep-brain-stimulation/