title: When should MERRF (myoclonus epilepsy associated with ragged-red fibers) be the diagnosis?
abstract: Myoclonic epilepsy associated with ragged red fibers (MERRF) is a rare mitochondrial disorder. Diagnostic criteria for MERRF include typical manifestations of the disease: myoclonus, generalized epilepsy, cerebellar ataxia and ragged red fibers (RRF) on muscle biopsy. Clinical features of MERRF are not necessarily uniform in the early stages of the disease, and correlations between clinical manifestations and physiopathology have not been fully elucidated. It is estimated that point mutations in the tRNALys gene of the DNAmt, mainly A8344G, are responsible for almost 90% of MERRF cases. Morphological changes seen upon muscle biopsy in MERRF include a substantive proportion of RRF, muscle fibers showing a deficient activity of cytochrome c oxidase (COX) and the presence of vessels with a strong reaction for succinate dehydrogenase and COX deficiency. In this review, we discuss mainly clinical and laboratory manifestations, brain images, electrophysiological patterns, histology and molecular findings as well as some differential diagnoses and treatments.
authors.affiliation: Departamento de Neurologia, Hospital de Clínicas, Universidade Federal do Paraná, Curitiba, PR, Brazil.
authors.forename: Paulo José
authors.initials: PJ
authors.lastname: Lorenzoni
authors.affiliation: Departamento de Neurologia, Hospital de Clínicas, Universidade Federal do Paraná, Curitiba, PR, Brazil.
authors.forename: Rosana Herminia
authors.initials: RH
authors.lastname: Scola
authors.affiliation: Departamento de Neurologia, Hospital de Clínicas, Universidade Federal do Paraná, Curitiba, PR, Brazil.
authors.forename: Cláudia Suemi Kamoi
authors.initials: CS
authors.lastname: Kay
authors.affiliation: Departamento de Neurologia, Hospital de Clínicas, Universidade Federal do Paraná, Curitiba, PR, Brazil.
authors.forename: Carlos Eduardo S
authors.initials: CE
authors.lastname: Silvado
authors.affiliation: Departamento de Neurologia, Hospital de Clínicas, Universidade Federal do Paraná, Curitiba, PR, Brazil.
authors.forename: Lineu Cesar
authors.initials: LC
authors.lastname: Werneck
mesh_terms: D003937:Diagnosis, Differential; D006801:Humans; D017243:MERRF Syndrome / Q000175:diagnosis* / Q000188:drug therapy / Q000235:genetics