Letter with reference to the article “Importance of electromyographic studies in the diagnosis of orthostatic tremor”

Sir,

We read with great interest the article published recently by Yagüe et al.¹ about the importance of electromyographic study in the diagnosis of orthostatic tremor. Our intention is not to assess the pathophysiological-diagnostic aspect of the article, brilliantly exposed by the authors who provide electromyographic concepts that demonstrate the growing and undeniable importance of electrophysiological analysis in the study of movement disorders. As the authors note, orthostatic tremor is an idiopathic motor disorder, although its possible association with pons lesions² or cerebellar degeneration^3,4 has been reported. Both of these constitute symptomatic forms of orthostatic tremor. It has been speculated that these anatomical structures (brainstem and cerebellum) could be directly involved in the pathogenesis and modulation of orthostatic tremor,^5,6 in a manner similar to what might happen in essential tremor.^7–9 We have noted that, in the case presented by Yagüe et al.,¹ the patient presented a deficiency of vitamin B12 in her medical history, and this has motivated us to write this letter to highlight the possible association existing between orthostatic tremor and vitamin B12 deficiency. Eleven years ago, our group published the case of a patient with orthostatic tremor who also suffered vitamin B12 deficiency.¹⁰ While we recognise that this association is difficult to justify from the standpoint of biological plausibility, the fact that, following the reinstatement of the deficient vitamin, the tremor disappeared does strengthen this causal association. Since then, other cases have been published in which vitamin B12 deficiency has been associated with tremor.^11,12 Furthermore, several neuroimaging studies have revealed abnormalities in the cerebellum and pons of patients with vitamin B12 deficiency.^13,14 We believe these studies lend plausibility to the hypothesis of there being a causal inference between vitamin B12 deficiency and orthostatic tremor.