Proliferative myositis and nodular fasciitis: a retrospective study with clinicopathologic and radiologic correlation

Abstract

Proliferative myositis (PM) and nodular fasciitis (NF) are two diseases easily misdiagnosed as cancer, often promoting unnecessary invasive procedures. To make accurate diagnoses of PM and NF and for the differential diagnosis between them, we performed a retrospective study to evaluate the roles of the clinical, radiologic, and pathologic characteristics of PM and NF. With an emphasis on the clinicopathologic and radiologic characteristics, we conducted a retrospective study of 8 cases of PM and 64 cases of NF that were diagnosed between 2012 and 2018. According to MRI findings, the lesions of PM and NF appeared as homogeneous masses with homogenous hypointensity or isointensity on T1-weighted images and as moderately or markedly hyperintense signals on T2-weighted images compared to skeletal muscle. In terms of histopathologic features, the differences between PM and NF mainly consisted of the presence of ganglion-like myofibroblasts with vesicular nuclei and basophilic cytoplasm in PM. The areas abundant in myxoid stroma with inflammatory infiltration that did not have abundant ganglion-like cells suggest NF. Immunohistochemically, the spindle-shaped cells of PM stained positive for smooth muscle actin (SMA), while the ganglion-like cells were negative. The spindle-shaped cells of NF showed diffuse expression of SMA, calponin, and vimentin. Our comprehensive study further demonstrated that PM and NF had a wide clinicopathologic and radiologic spectrum. Correlation with the clinical, radiologic and pathologic characteristics may help clinicians and pathologists make accurate diagnoses.

Keywords: Proliferative myositis; clinical characteristics; nodular fasciitis; pathology; radiological characteristics.

Figure 1

Radiologic examinations of PM and NF. A-C. MRI examinations of PM. A 4-year-old girl with an irregular soft tissue mass in the right hip muscle. A. T1WI showed mainly isointense signal and a small patch of slightly high signal. B. T2WI showed high signal, with empty blood vessels. C. Enhanced scanning showed significant enhancement and enhanced vascular shadows. D, E. CT examinations of PM. A 28-year-old man with a mass in the right front chest wall. D. A mass with a CT value of 16 Hu, uneven density, unclear boundaries, and expansive growth. E. The mass invaded the fifth front rib, with significant bone destruction. F, G. MRI examinations of NF. A 44-year-old woman with irregular soft tissue masses on the left side of the armpit. F. Enhanced scanning with significant enhancement and tortuous vascular shadows. G. T2WI showed high signal in the lesion, with empty blood vessels. H. CT examinations of NF, A 56-year-old man with a mass in the right front chest wall. A large soft tissue mass next to the right small chest muscle; the signals from the lesions were isodense compared with those from the adjacent muscles.

Figure 2

Pathologic examinations of PM and NF. A-D. A 57-year-old woman with a mass in the left thigh. Microscopic examination revealed proliferating spindle-shaped cells, checkerboard-like pattern, and larger basophilic cells that resemble ganglion cells, which are diagnostic features for PM. A. Low-power microscopy view of proliferative myositis. The muscle bundles are separated by endomysial, perimysial, and epimysial proliferation of fibrous connective tissue in a checkerboard-like pattern (hematoxylin-eosin, original magnifications × 100). B. Medium-power microscopy view of proliferating spindle-shaped cells and skeletal muscle fibers with secondary atrophy (hematoxylin-eosin, original magnifications × 200). C. High-power microscopy view of basophilic ganglion-like cells (hematoxylin-eosin, original magnifications × 400). D. Ganglion-like basophilic giant cells or ganglion-like myofibroblasts in the area of mucoid degeneration (hematoxylin-eosin, original magnifications × 200). E-G. A 40-year-old woman with a mass in the chest wall. Microscopic examination revealed areas of uniform bland spindle cells that are arranged in short intersecting fascicles within a loose stroma accompanied by extravasated erythrocytes and scattered lymphocytes, which are diagnostic features for NF. E. The lesion was composed of spindle-shaped cells with abundant elastic fibers. The spindle-shaped cells grew in a mucus-like matrix and had irregular infiltrative margins partially extending into the adipose tissue (hematoxylin-eosin, original magnifications × 100). F. Proliferating spindle-shaped cells are arranged in bundles and interlaced bands (hematoxylin-eosin, original magnifications × 100). G. Spindle-shaped cells indicate the proliferation of fibroblasts or myofibroblasts without hyperchromasia or pleomorphism. Extravasated red blood cells are also present (hematoxylin-eosin, original magnifications × 400). H-K. Immunohistochemical results of PM. A 57-year-old woman with a mass in the left thigh. H. The spindle-shaped cells stained diffuse positive for SMA (original magnifications × 200). I. The ganglion-like cells were negative for SMA (original magnifications × 400). J. PM was negative for myoglobin (original magnifications × 200). K. PM was negative for myoD1 (original magnifications × 200). L-O. Immunohistochemical results of NF. A 31-year-old man with a mass in the right thigh. L. The spindle-shaped cells were diffuse positive for SMA (original magnifications × 200). M. The spindle-shaped cells were positive for calponin (original magnifications × 200). N. The spindle-shaped cells were negative for desmin (original magnifications × 200). O. The spindle-shaped cells were negative for CD34 (original magnifications × 200).