The inventors initially participated to the identification of LPIN1 mutations as a cause for massive rhabdomyolysis episodes in children, triggered by febrile illness. The inventors have suggested that TLR9 antagonists would be suitable for the treatment of rhabdomyolysis (WO2017085115). The inventors thus treated 2 patients with lipin-1 disease by a TRL9 antagonist (hydroxychloroquine). They showed that the accumulation of mtDNA in plasma of the two patients before treatment decreases under treatment. When the treatment was stopped, the accumulation of mtDNA reappeared, then normalized when treatment was resumed. Accordingly, the present invention relates to a method for determining whether a patient suffering from rhabdomyolysis achieves a response with a TLR9 antagonist comprising determining the amount of mitochondrial DNA (mtDNA) in a blood sample obtained from the patient (e.g. by PCR).