Objective: To report two cases of adult-onset KMT2B related dystonia treated with pallidal deep brain stimulation (DBS).

Background: KMT2B gene mutations have been described as a new cause of progressive generalized dystonia usually of childhood onset and typically starting as lower limb dystonia that spreads to generalized dystonia in a few years.

Method: we present two cases of siblings with adult-onset axial dystonia related to pathogenic heterozygous variant in KMT2B gene treated with bilateral internal globus pallidus (GPi) DBS.
First case is a 56 years-old female with mood disorder and mild obsessive control disorder. At age 52, she noticed backwards cervical spasms and cervical pain mainly during walking that progressed in 18 months to severe cervical and axial spasms affecting her daily activities.
Second case, is a 38 years-old brother with no relevant medical history. At age 36 he started with axial and retrocollis spasms when standing, walking, running, even when laying, that worsened over time interfering his daily activities. In both cases, there was no response to pharmacological treatments, including botulinum toxin injections, so GPi-DBS was decided.
Under general anaesthesia, bilateral electrodes (Medtronic® 3389) were implanted into bilateral GPi and connected to a neural stimulator (Medtronic® ACTIVA RC). Post-surgery cranial MRI was performed showing a correct placement of the electrodes and no complications.

Results: In the first case, after two months of DBS surgery, patient presented a significant improvement of dystonia with only occasionally retrocollis spasms. The improvement was maintained in last follow-up (24-months). In the second case, he presented a moderate improvement but still showed cervical spasms during walking, so he still needed DBS setting adjustments in last follow-up (12 months).

Conclusion: Dystonia due to KMT2B mutations present a poor response to anti-dystonic drugs. GPi-DBS surgery is a good therapy option for KMT2B related dystonia as shown in our cases and previous reports.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/deep-brain-stimulation-response-in-siblings-with-kmt2b-dystonia/