Cerebellar mutism: definitions, classification and grading of symptoms

Abstract

Dear editor, We would like to thank Dr. Frassanito and Dr. Massimi for their interesting and valuable comments on our review article on cerebellar mutism, particularly in sharing their own operative experience [1]. However, their interpretation of the incidence of cerebellar mutism syndrome, following surgery for cerebellar ependymoma in von Hoff's article, seems to be based on a misunderstanding regarding definitions of two different problems related to the cerebellum in this article—“postoperative cerebellar mutism” versus “postoperative cerebellar syndrome”. von Hoff et al. define the “cerebellar syndrome” as a motoric triad of ataxia, nystagmus, and dysmetria, grade it as mild, moderate, or severe as proposed by Riva et al. in 1991 [2] and refer to it as a general measure of cerebellar damage. They do not relate it to the wellrecognized posterior fossa/cerebellar mutism syndrome as such. Thus, a closer look at Table 1 reveals that the incidence of postoperative cerebellar mutism was in fact 0 [3]. The same motoric cerebellar syndrome is described in a group of patients as a measure of pre-operative clinical status in another article by Callu et al from 2009. The incidence of ataxia, nystagmus and dysmetria before surgery was 31%, while the incidence of post-operative mutism was 8% [4]. In both series, the telovelar approach was used from year 2004 and onwards, but only in patients whose tumor was located in the inferior part of the vermis. This was recommended after recognizing the role that splitting of the vermis plays in post-operative intellectual impairment [5]. This discussion highlights the confusion that exists in the literature regarding classification and definitions. We have defined “cerebellar mutism” as muteness following lesion of the cerebellum as opposed to the cerebrum or the lower cranial nerves. It is further characterized by delayed onset, limited duration, and (usually) long-term linguistic sequelae [6]. A common synonym is “transient cerebellar mutism” [7]. The “posterior fossa syndrome” is a broad term that usually includes cerebellar mutism as its main feature, but also encompasses motoric problems such as ataxia, hypotonia, cranial nerve palsies together with neurobehavioral abnormalities such as emotional lability, poor oral intake, decreased spontaneous initiation of movements, and impaired eye opening [8]. The “cerebellar mutism syndrome” was initially used as a synonym for isolated cerebellar mutism [9, 10], but has more recently in T. Gudrunardottir :A. Sehested :K. Schmiegelow (*) Department of Pediatrics, University Hospital Rigshospitalet, Copenhagen, Denmark e-mail: kschmiegelow@rh.dk