Brain ¹⁸F-FDG PET Metabolic Abnormalities in Macrophagic Myofasciitis: Are They Stable?

TO THE EDITOR: We are writing this letter as an addition to our recently published study (1). Our aim is to add some insight to the evolution of the brain abnormalities that are observed with macrophagic myofasciitis (MMF). MMF is a chronic disease whose evolution is slow and whose symptoms may first occur months to years after a vaccination containing aluminum hydroxide adjuvant particles (2). Nevertheless, the evolution of MMF is not fully understood or known. MMF-associated cognitive dysfunction is based on a tripod combining dysexecutive syndrome, memory impairment, and interhemispheric disconnection. One pilot study suggested that MMF-associated cognitive dysfunction appears to be clinically stable over time (3), and a recent study evaluating a support vector machine classifier suggested that the abnormalities observed with ¹⁸F-FDG PET may be sensitive and can be used to monitor patients.

In order to evaluate the evolution of ¹⁸F-FDG PET brain metabolic abnormalities, we retrospectively included 18 patients on whom an additional follow-up ¹⁸F-FDG PET brain scan was performed because of persisting cognitive complaints (median age, 56.9 y [range, 22.3–66.2 y]). ¹⁸F-FDG PET was performed following the same brain protocol acquisition as previously described (1). The Institutional Review Board (Comité de Protection des Personnes Ile-de-France VI), taking into account the retrospective nature of the study, approved the protocol (December 18, 2013) without requiring informed consent by the patients. The median time between the two examinations was 32.9 mo (range, 6.4–48.6 mo). Using analysis of covariance and negative or positive contrast in SPM12, we generated a t test mask by comparing the mean of the first cerebral ¹⁸F-FDG PET acquisition with that of the second. The results of the comparison were collected at a P value of less than 0.005 at the voxel level, for clusters of at least 200 voxels (corrected for cluster volume).

Brain abnormality maps did not show any statistically significant negative or positive metabolic difference between the two examinations, confirming the idea that MMF is a slowly progressive or nonprogressive disease, in concordance with the fact that neurologic symptoms—even if they fluctuate—do not worsen or improve over time.

• © 2017 by the Society of Nuclear Medicine and Molecular Imaging.