Intensification of an Essential Tremor by SARS-CoV-2.

We read with interest the article by Passaretti et al. about a 60-year-old male with a previous history of essential tremor since age 17 years who experienced worsening of the postural and kinetic tremor with left-sided predominance three weeks after an asymptomatic SARS-CoV-2 infection [1]. It was concluded that SARS-CoV-2 infections may worsen essential tremor due to virus-induced immune-mediated functional impairment of cerebellar networks [1]. The study is appealing but raises concerns that need to be discussed.

The first magnetic resonance imaging (MRI) showed left pontine small lacunas [1]. However, no explanation for this abnormal finding was provided. Furthermore, these lacunas were not mentioned in the second MRI carried out after worsening of the tremor [1]. An explanation of the lacunas should be provided, particularly if they were the residual condition of previous ischemic stroke, bleeding, trauma, metabolic disturbance, or hypoxia. We thus should be informed about the classical cardiovascular risk factors of the index patient, such as atrial fibrillation, diabetes, smoking, hypertension, infection, or hyperlipidemia. Missing is the previous history of the index case in this respect. We should be told if the previous history was positive for neurological disease in addition to essential tremor.

Missing is the information whether the two MRIs were carried out with or without application of contrast medium. Application of contrast medium is crucial to assess if there was brainstem encephalitis [2], rhombencephalitis [3], limbic encephalitis [4], or cerebellitis [5], as all these conditions have been previously reported as complications of SARS-CoV-2 infections.

Missing is the report about the long-term outcome of the positional and kinetic tremor. We should be told if the pre-infectious intensity of the tremor was reached again at the last follow-up.

We should be told why the patient was not treated with steroids or immunoglobulins. Since an abnormal immunological reaction is the most likely cause of the worsening tremor, it would have been indicted to apply immune modulating treatment to assess if such a therapy was beneficial or not.

A shortcoming of the study is that the patient did not undergo investigations of the cerebrospinal fluid (CSF). CSF investigations are obligatory to exclude aseptic pleocytosis, immune encephalitis, or SARS-CoV-2-associated meningitis.

Since the patient experienced relief of the tremor under alcohol, we should be told whether he drank alcohol regularly and if there was hepatopathy or hepatic encephalopathy, which could explain the worsening of the tremor as well.

We do not agree with the statement that inflammatory findings more likely confine to the cerebellum or the brainstem [1]. Immune encephalitis following a SARS-CoV-2 infection can occur in all cerebral locations.

Overall, the interesting study has some limitations and inconsistencies that call the results and their interpretation into question. Clarifying these weaknesses would strengthen the conclusions and could enhance the study.