Can FDG PET/CT imaging have a role in clinical cases of Dermatomyositis?

Introduction: The purpose of this educational exhibit is to review and convey the latest findings in the literature regarding the clinical usefulness of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in dermatomyositis.

Methods: Several large scientific databases, including PubMed, Web of Science, and Google Scholar, were used to accumulate review articles and scientific communications relating to the clinical PET practices in imaging neurofibromas. Next, review articles and scientific studies were compiled from the databases to accumulate a comprehensive body of literature. Specifically, articles will encompass today’s knowledge of dermatomyositis as derived from PET studies and reflect the most recent innovations in the molecular imaging with PET of dermatomyositis.

Results: FDG PET/CT can serve as a vital imaging modality in diagnostic and prognostic evaluation of dermatomyositis due to its ability to detect inflammation. Several studies have concluded that levels of biochemical markers of dermatomyositis, such as cytokeratin and creatine kinase, correlate with FDG PET semi-quantitative parameters. These studies have also proposed that FDG PET parameters (such as SUVmean, SUVmax, and the ratio of SUVmax in proximal muscles over SUVmax of the longissimus thoracis muscle) can be used to differentiate dermatomyositis from other nonspecific inflammatory diseases and evaluate anti-inflammatory therapeutic efficacy.

Dermatomyositis can be associated with underlying malignancies, and multiple findings in the literature suggest that FDG PET can aid clinicians in identifying underlying malignant tumors that may not have been otherwise detected by lab findings. Some of the reported literature have asserted that FDG PET/CT may serve as a ‘one-stop-shop’ for dermatomyositis as it has helped clinicians diagnose and monitor the progression of dermatomyositis, and has highlighted underlying lung carcinoma, adenocarcinoma of the mediastinum, and occult ulcerative colitis in their respective dermatomyositis study subjects. Introducing FDG PET/CT imaging in the management of dermatomyositis may help identify patients who require earlier intervention.

Several case reports have reported that FDG PET/CT patterns detected metabolic activity prior to patients exhibiting signs of impairment due to interstitial lung disease (ILD), one of the highest causes of mortality in dermatomyositis patients. One specific case study describes a patient who suffered from ILD but expired due to late treatment intervention. This patient was reported to have had significantly higher metabolic activity detected by FDG PET prior to ILD symptoms arising, and the clinicians reported that FDG PET detected signals corresponding to ILD well before any other functional modalities and lab values did. FDG PET has also been shown to detect extensive calcinosis in dermatomyositis patients who have normal creatine kinase levels. All these studies have concluded that FDG PET is valuable in assessing extent of calcinotic inflammation in dermatomyositis patients, especially if creatine kinase levels cannot be used as a prognostic marker.

Conclusions: A review of literature found that FDG PET/CT can provide vital functional and metabolic information in a systemic inflammatory disease like dermatomyositis. FDG PET/CT has the potential to not only make diagnosis of dermatomyositis easier for clinicians, but also uncovering underlying malignancies in dermatomyositis patients that may not have been detected otherwise on physical exam or labs. Progression to ILD in dermatomyositis patients incurs greater risk of mortality, but reliable biomarkers that herald progression to ILD can indicate need for earlier medical intervention. Currently a large amount of the recent literature pertaining to FDG PET/CT and dermatomyositis consists primarily of case reports. Further studies are warranted to investigate the usefulness of FDG PET/CT in clinical care and management of dermatomyositis patients.