Holmes tremor (HT) is a low-frequency (<4.5 Hz) and large-amplitude tremor that is usually present at rest and accentuated by action.1 The underlying pathophysiological mechanism that leads to HT involves different lesions affecting the brainstem that damage the ascending cerebellothalamic and dentate-rubro-olivary pathways, and nigrostriatal fiber tracts.2 HT is generally the result of lesion(s) such as stroke, trauma, and/or demyelinating diseases.1 Here, we describe the case of a patient who developed HT after a direct lesion of the midbrain, an etiology rarely reported in the literature.

A 31-year-old male was taken to the emergency department after being stabbed in the right eye. He was conscious but presented with left hemiparesis. The initial brain computed tomography was normal. A few days later, at discharge, the left hemiparesis had partially improved and he was able to walk, albeit with slight difficulty. Two months later he developed a tremor in his left arm at rest, which was exacerbated with posture and additionally worsened with action. Brain magnetic resonance imaging (MRI) revealed a right midbrain injury and the trajectory of the knife reaching the midbrain (Figure 1). He was treated with propranolol without an effective response. After the introduction of biperiden 6 mg/day the tremor improved, remaining stable for the next 3 months of follow-up.

Despite the rarity of this case, clinicians working with persons with brain injuries should be aware of this type of situation. The singularity of the report is also because this stabbing injury crossed the orbit, reaching directly to the midbrain, without affecting other important nearby structures.

A delayed onset between the lesion and the occurrence of tremor has been reported in the literature, as observed in the present case, and could be related to receptor sensitivity changes or axonal sprouting, which may lead to a rearrangement of the central pathways in the brain or to an aberrant neuronal reorganization, resulting in plasticity.2,3

Once established, post-traumatic HT rarely remits. Treatment is difficult and few cases respond well to primidone and propranolol. Interestingly, the present patient responded well to Biperiden, which is not the first-line therapy but occasionally anticholinergics may help.3 Finally, because of refractory symptoms and tremor severity in some cases, stereotaxic surgery may be contemplated. To date, there is no evidence whether the response of HT to treatment varies depending on the etiology or location and reporting such differences would contribute to the care of patients with this condition.