Fragile X-associated tremor ataxia syndrome (FXTAS) is a genetic disorder caused by a FMR1 gene premutation; it can result in severe intention tremor and cerebellar ataxia. Neuroimaging and histopathology studies suggest a dysfunction of the rubro-olivo-cerebellar loop. 1 The tremor can become pharmacoresistant. Bilateral thalamic stimulation did not demonstrate any clear benefit on FXTAS tremor, and in some cases it was associated with a decline of ataxia, language, and cognitive function. [2][3][4] Compared to unilateral stimulation, bilateral thalamic stimulation induced more adverse events and appeared to be more prevalent in patients displaying cognitive deficits or multiple magnetic resonance imaging (MRI) abnormalities. 5 Therefore, in a 61-year-old FXTAS patient presenting with an intractable tremor, we decided to implant an electrode unilaterally.
The patient's medical history primarily included hemorrhagic stroke within the right cerebral peduncle at the age of 50 years, with no sequela. The diagnosis of FXTAS was definite: genetic testing revealed an FMR1 premutation bearing 95 6 5 repetitions of CGG; and the 2 main clinical criteria of FXTAS, tremor and ataxia, were present, in addition to 1 minor clinical criterion, moderate working memory deficit, and all the radiological criteria 1 (Fig. 1). Symptoms started 5 years ago at the age of 56 years.
Neurological examination and electrophysiological recordings showed a low-frequency (3.3 Hz) tremor predominant to the left superior limb (rated 15/24 left vs 13/24 right on Fahn score), mainly proximal but also distal, both intentional and postural (rated 15/24 vs 14/24, respectively), and with no rest component. There was no inferior limb postural, intention, or orthostatic tremor. It was incapacitating and pharmacoresistant. Cerebellar ataxia score was elevated at 18/40 on the scale for the assessment and rating of ataxia (SARA; 8-item scale measuring gait, stance, sitting, speech disturbance, finger chase, nose-finger test, fast alternating hand movements, and heel-shin slide), validated for spinocerebellar and nonspinocerebellar ataxia patients. 6 dopamine transporter (DAT) scan was normal.