Clinical value of a [18F]-FDG PET-CT muscle-to-muscle SUV ratio for the diagnosis of active dermatomyositis.

OBJECTIVE: To study a muscle-to-muscle standardised uptake value (SUV) ratio with FDG-PET/CT (FDG-PET) as a marker for the detection of disease activity in dermatomyositis (DM). METHODS: Patients with DM (n = 24) who met the European Neuro-Muscular Centre diagnostic criteria were retrospectively identified over a 3-year period through a national survey. Muscle biopsy was performed in all patients. Maximum SUV was measured in proximal muscles (SUVPROX) that had the highest radiotracer uptake on visual grading as well as in the musculus longissimus thoracis (SUVMLT), whereas mean SUV was measured for the liver (SUVLIV). Muscle-to-liver SUV ratios for either muscle group were compared and a SUVPROX/SUVMLT ratio was calculated. SUVPROX/SUVMLT of DM patients were compared with age- and sex-matched control subjects (n = 24) with melanoma who had received FDG-PET scans. RESULTS: DM patients presented with proximal and symmetrical muscle uptake. Differences in SUVPROX/SUVLIV and SUVMLT/SUVLIV ratios in DM subjects were significant (p < 0.001). SUVPROX/SUVMLT ratios in DM and their controls also differed significantly (p = 0.0012). The SUVPROX/SUVMLT ratio threshold between DM subjects and controls was 1.73 with a sensitivity of 50% (CI95%, 29.1 to 70.9%) and specificity at 83.3% (CI95%, 62.6 to 95.3%). When amyopathic DM patients were removed from the analysis, specificity was increased to 95% (CI95%, 75.1 to 99.9%) with a likelihood ratio of 10 and an AUC of 83.4% (CI95%, 71.4 to 95.4%). CONCLUSION: A muscle-to-muscle SUVPROX/SUVMLT ratio with a cut-off value of 1.73 in FDG-PET imaging might serve as a non-invasive marker to determine disease activity in dermatomyositis. KEY POINTS: • [18F]-FDG PET-scanner standardised uptake value (SUV) could reflect disease activity in dermatomyositis (DM). • A ratio of SUV in proximal muscles (SUVPROX) to SUV in musculus longissimus thoracis (SUVMLT) could be used to determine active DM. • Active disease is suspected for SUV PROX /SUV MLT ratios greater than 1.73.

Perfusion SPECT findings in a suspected case of Rasmussen encephalitis.

We report the case of a 35-year-old who was referred for brain perfusion single photon emission computed tomography (SPECT) for pharmacoresistant epilepsy. Her medical history included brain surgery for an inflammatory lesion of unknown origin at age 23 before partial epilepsy occurred. The seizures became refractory to standard antiepileptic drugs and she developed epileptic negative myoclonus of the right upper limb, nocturnal motor seizures, and progressive intellectual impairment. Neurological symptoms slowly worsened with mild aphasia and right visual neglect. Inter-ictal brain SPECT showed decreased cerebral blood flow on the left hemisphere corresponding on magnetic resonance imaging (MRI) with moderate left hemiatrophy, a left frontal defect in accordance with the history of surgery, and a crossed cerebellar diaschisis. Clinical and imaging data were in favor of a late-onset form of Rasmussen encephalitis. Rasmussen syndrome is a rare unilateral devastating disease with childhood onset that can also occur in adulthood, characterized by intractable epileptic seizures associated with progressive neurological deterioration and unilateral progressive atrophy. Brain perfusion SPECT can speed up the diagnosis when exhibiting a strictly unilateral hemispheric hypoperfusion in such a clinical context. It can also guide brain biopsy in cases of inconclusive MRI.