It has always been puzzling why tumors of the basal ganglia and thalamus present rarely with dystonia, tremor or chorea, while discrete lesions in particular certain areas of the structures pertaining to the cortico-basal ganglia-thalamic-cortical circuitry are well known to underly the development of movement disorders [5, 6]. In our case, the unusual temporal course of appearance and disappearance of hemidystonia along with the changes in imaging, nevertheless allows to draw several conclusions.
While movement disorders may rarely be caused primarily by the tumor affecting the subcortical sensorimotor loop [2–4], they may also appear subsequently to specific treatment measures including surgery, chemotherapy or targeted radiotherapy [3, 4]. This has been exemplified by a recent study of Sadighi et al reporting two patients in whom dystonia became manifest only after removal of thalamic tumors in a cohort of 83 patients [4]. Of note, in our case dystonia became manifest only after radiotherapy lead to a marked reduction of the tumor volume but resulting in a thalamic lesion.
Previous studies have shown that hemidystonia most often is associated with lesions of the anterior putamen often combined with lesions of the caudate, while thalamic lesions have been observed more rarely [5]. The most common manifestation of dystonia secondary to thalamic lesions in focal hand dystonia, occasionally associated with sensory deficits, but few cases of hemidystonia have been described as well [6, 7]. While various sites in the thalamus have been described to be involved, our case clearly demonstrates a discrete lesion affecting both the ventral posterolateral and the intralaminar thalamus.
In several instances as of hemidystonia described earlier that a pre-existent or concomitant hemiparesis was an accompanying feature indicating involvement of the posterior limb of the internal capsule [7]. While it is possible that the phenomenological appearance of dystonia is simply overshadowed by the presence of motor weakness, it has also been postulated that dystonia may be the result of faulty reorganization of subcortical circuitries in the presence of lesions in the sensorimotor loop. The dynamics in our case suggests that both are relevant.
The prognosis of movement disorders associated with pediatric thalamic tumors is quite variable [3, 4]. The effect of medication is limited [3, 4]. The primary concern is to obtain control of tumor growth. As shown here, the later may be the primary determinant for the dynamics of the movement disorders in such cases.