Two-step differentiating criteria for distinguishing atypical MELAS from classic MELAS^{^a}

Finding Category	Findings	Score
Step 1
Demographic	First strokelike episode at younger than 10 years of age	+1
Clinical	Vision loss at strokelike episode onset	−1
Clinical	Overlap with LS spectrum	+2
Clinical	SNHL	−2
Clinical	Developmental delay	+1
Neuroimaging	Scattered, anterior/cerebellar lesions	+1
Neuroimaging	Presence of large CSLLs (>30 mm)^{^b}	−1
Step 2 (If −1 ≤score≤ 1)
Genetic	Respiratory chain subunit gene group is most likely associated with atypical MELAS; mt-tRNA genes group is most likely associated with classic MELAS

↵a Score ≥2: atypical MELAS, score ≤ −2: classic MELAS. If −1 ≤score≤ 1: equivocal (genetic study should be considered) →Step 2.
↵^bCSLLs measured in their largest anterior-posterior extension in the axial plane using FLAIR and/or DWI sequences.