Keywords
F18-FDG-PET/CT, Antisynthetase Syndrome, Fasciitis
Introduction
More prevalent in women than men, Antisynthetase Syndrome is rare and poorly defined autoimmune disease associated with interstitial lung disease, polymyositis, and dermatomyositis. In addition to a variety of diagnostic tools, imaging modalities are needed in certain situations. A 42-year-old woman with Anti-Jo-1-positive Antisynthetase Syndrome presented with thoracic muscular pain. She underwent whole-body Fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) in order to evaluate the total extent of the muscles affected. Depicting symptomatic symmetric myositis of the intercostal muscles, the examination additionally revealed unusually extensive fasciitis of the lower extremities.
Case Report
A 42-year-old woman presented with the history of unknown muscle pain, especially in the thighs and upper arms during pregnancy. Due to placental infarction a caesarean section was performed. Afterwards, a muscle biopsy revealed endomysal inflammation of the striated muscles as well as elevated anti-Jo-1-antibody confirming the suspected polymyositis. Therapy with cortisone, methotrexate and tacrolimus was started, which did not bring any improvements. Six years later, the patient experienced an onset of shortness of breath with hardly any improvement on inhalation therapy. Lung function was stabilized under belimumab therapy. Recently, the patient developed pains in shoulders and arms, paravertebral muscles and the chest wall with worsening during nighttime and morning stiffness. Thorax and shoulder Magnet Resonance Imaging (MRI) were indecisive. F18-FDG PET/CT examination was then requested to assess the extension of disease. [Fig. 1] showed bilateral muscular tracer uptake affecting the shoulder rotator cuff, synovia of both shoulder joints and the dorsolateral intercostal musculature, consistent with myositis (A and B, arrows). Additionally, PET/CT demonstrated significant bilateral fascial uptake of the lower extremity and the left knee joint (C, arrow). No marked tracer uptake of the large arterial walls was detected. Transversal images depicted extensive bilateral tracer uptake along the fascial compartments of the hip and thigh muscles particularly in the hamstring muscles consistent with fasciitis. A faint patchy FDG activity in the dorsal of the lungs confirmed the known lung involvement (B, block arrow). An incisional biopsy of the left thigh was performed. Macroscopy revealed chronic-active inflammatory changes with ligamentous fibrosis. Immunohistochemistry showed predominantly CD4-positive T-lymphocytic inflammatory infiltrates.
Fig. 1 PET with corresponding fusion PET/CT image with F18-FDG of upper thorax including shoulder rotator cuff, synovia of both shoulder joints A and of dorsal patchy affection of the disease with intercostal muscle involvement B and extended involvement of the lower extremities C.
Discussion
Antisynthetase Syndrome is a rare and poorly defined autoimmune disease associated with interstitial lung disease, polymyositis, and dermatomyositis [1]
[2]
[3]
[4]
[5]
[6]. MRI can help differentiating fatty muscle lesions from inflammatory changes; however, the ability to perform a whole-body examination is restricted. Therefore F18-FDG can be useful in patients with inflammatory muscle diseases and allows FDG uptake measurement with Standardized Uptake Value (SUV) for a base-line diagnostic and therapy response [2]. There are very few cases reporting unusual pattern of FDG uptake in the muscle and fascia in inflammatory muscle diseases [3]
[4]
[5]
[6]. The pattern of FDG uptake similar to our patient’s was reported with either focal or lymph node involvement [7]
[8]; however in the presented case patchy lung tracer uptake along with longitudinal muscle and fascia inflammation corresponded to all manifestations of the disease.
