Objective: To explore the possibilities of radioligands against the mitochondrial outer membrane protein TSPO as biomarkers for mitochondrial disease, we performed positron emission tomography (PET)-MR brain imaging with [¹¹C]PK11195 in 14 patients with genetically confirmed mitochondrial disease and 33 matched controls.   

Methods: A case-control study of PET-MR imaging with the TSPO radioligand [¹¹C]PK11195. 

Results: 46% of symptomatic patients had volumes of abnormal radiotracer binding greater than the 95^th percentile in controls. [¹¹C]PK11195 binding was generally greater in grey matter and significantly decreased in white matter. This was most striking in patients with nuclear TYMP or mitochondrial m.3243A>G MT-TL1 mutations, in keeping with differences in mitochondrial density seen post mortem. Some regional binding patterns corresponded to clinical presentation and underlying mutation, even in the absence of structural changes on MRI. This was most obvious for the cerebellum, where patients with ataxia had decreased binding in the cerebellar cortex, but not necessarily volume loss. Overall, there was a positive correlation between aberrant [¹¹C]PK11195 binding and clinical severity. 

Conclusion: These findings endorse the use of PET imaging with TSPO radioligands as a non-invasive in vivo biomarker of mitochondrial pathology.

Classification of Evidence: This study provides Class III evidence that PET-MR brain imaging with TSPO radioligands identifies mitochondrial pathology.