Is the spinal cord truly affected in half of the patients with Kearns-Sayre syndrome?
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LETTER TO THE EDITOR
Is the spinal cord truly affected in half of the patients with Kearns-Sayre syndrome? Josef Finsterer 1 Received: 30 July 2020 / Accepted: 6 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
With interest we read the article by Luca et al. about a retrospective study of 11 patients with Kearns-Sayre syndrome (KSS) who had undergone MRIs of the spinal cord during the observational period [1]. Spinal cord involvement in the disease was detected in 6 patients but was absent in 5 patients. It was concluded that KSS patients frequently develop spinal cord involvement and that workup of KSS patients should include spinal MRI. We have the following comments and concerns. Spinal cord involvement has been seldomly reported in KSS although the causative mtDNA deletion can be detected in the spinal cord. On the contrary, spinal cord involvement is a frequent feature of mitochondrial encephalopathy, lactic acidosis, and stroke-like episode (MELAS) syndrome or leukoencephalopathy with brainstem and spinal cord involvement (LBSL). We should know whether the authors considered a double trouble and whether pathogenic variants in the MT-TL1 gene and the DARS-gene were excluded. Missing are also cerebrospinal fluid (CSF) investigations to exclude differentials such as acute disseminated encephalomyelitis, multiple sclerosis, or neuromyelitis optica spectrum disorder. Kearns-Sayre syndrome may manifest with elevated lactate in the CSF [2]. We should know in how many of the 11 included patients CSF lactate was elevated by direct measurement in the CSF or by MR spectroscopy and whether the degree of spinal cord involvement was related to the CSF lactate levels. In 4% of the patients carrying a single mtDNA deletion, the mutation is inherited from the mother’s side [3]. We should know in how many of the 11 KSS patients the family history was positive and whether any of the 11 patients’ mothers were genetically tested.
The spinal cord lesion with sudden onset and partial remission presented in Fig. 2 is interesting. Since KSS may manifest with stroke-like episodes (SLEs) [4] and SLEs show up with an equivalent, dynamic lesion on MRI (stroke-like lesion (SLL)), we should know whether the authors considered the sudden deterioration in this particular patient as SLE and the lesion presented in Fig. 2 as SLL. SLLs typically present with hyperintensity on T2-weighted images, diffusion weighted imaging, and perfusion imaging, as hyper-, iso-, or hypointensity on apparent diffusion coefficient maps, and hypointensity on oxygen-extraction fraction MRI. Missing in this study are the heteroplasmy rates of the mtDNA deletions. Heteroplasmy rates may strongly determine the phenotypic expression of an mtDNA mutation [5]. Thus, we also should know heteroplasmy rates of the mtDNA deletion of all 111 patients, whether the mtDNA deletion was detected in the CSF, and whether the degree of spinal cord involvement correlated with heteroplasmy rates or the size of the mtDNA deletion. Overall, the interesting stu
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