Focal myositis--a pseudotumoral lesion

Focal myositis: a rare case report

Focal myositis is an uncommon, self-limiting, benign skeletal muscle disease, which is generally determined as an inflammatory pseudotumor. The etiology is not fully known, although it has been suggested that subclinical damage may play a role. As it leads to a tumoral mass it may be confused with several diseases leading to incorrect evaluations. Definitive diagnosis is made by biopsy of the skeletal muscle. In radiologic diagnosis, magnetic resonance imaging is the most important modality. In this paper we presented the imaging findings of a 58-year-old female patient with focal myositis who was admitted with complaints of forearm swelling.

Self-resolving focal non-ossifying myositis: a poorly known clinical and imaging entity diagnosed with MRI

Background

Focal myositis is a rare benign inflammatory pseudotumor, presenting as a painful nodular mass within a muscle, and characterized by spontaneous resolution within weeks.

Purpose

To assess the clinical and imaging findings of focal nodular myositis simulating a neoplasm at clinical examination, with no history of trauma.

Material and Methods

This study describes the locations and appearance at ultrasonography (US), computed tomography (CT), and magnetic resonance imaging (MRI) of this condition in a series of five patients.

Results

MRI and US displayed a solid intramuscular “tumor” and suggested a continuum between the proximal and distal muscle fibers that appeared thickened within the nodular lesion, a sign that has been reported in myositis ossificans. MRI showed edema in adjacent muscles and soft tissues, as well as intense enhancement of the mass. Intense vascular flows were seen at Doppler analysis. CT did not reveal the appearance of peripheral ossifications, ruling out the diagnosis of myositis ossificans. In some patients, the diagnosis of sarcoma had been suggested as possible by the radiologist. Imaging follow-up with MRI showed complete resolution of the masses over several weeks, thus avoiding a biopsy; no recurrence was observed at long-term follow-up (more than 24 months).

Conclusion

This paper highlights MRI and US findings in focal non-ossifying myositis, and emphasizes the role of MRI in suggesting this diagnosis, leading to the careful follow-up of the lesion until its resolution, and ruling out more aggressive lesions.

Focal myositis: a clinicopathologic study of 115 cases of an intramuscular mass-like reactive process

BACKGROUND

Focal myositis is an uncommon inflammatory pseudotumor of skeletal muscle that can be confused with a variety of neoplastic and inflammatory diseases. It is often misunderstood because it presents as a tumor-like mass, but histologically resembles a skeletal muscle myopathy or dystrophy. We wanted to discuss the detailed morphologic and immunophenotypic features of the largest reported group of focal myositis patients.

DESIGN

Two hundred and six cases coded as "focal myositis" were culled from our files. Only 115 cases with adequate material, a solitary lesion, and correct diagnosis were included. A variety of immunohistochemical studies were performed, as were polymerase chain reaction for T cell receptor gene rearrangement and immunoglobulin heavy chain rearrangement.

RESULTS

Age ranged from 7 to 94 years (mean 41, median 36 y). Most patients were otherwise healthy, and with the exception of 10 cases, lacked antecedent trauma. Masses that ranged in size from 1.0 to 20.0 cm (median 3.0 cm, mean 3.9 cm) were reported in specific muscles of the lower extremities (including vastus lateralis, adductor muscle, and groin muscles, n=39; gastrocnemius, n=22), followed by the trunk, neck (mentalis, n=8; sternocleidomastoid muscle, n=8), and upper extremity. Histologically, these were solitary intramuscular processes composed of variable myopathic (93%) and focal neurogenic (89%) changes, fibrosis, and inflammation (97%), occasionally accompanied by prominent eosinophils (n=20). By immunohistochemistry, most cases had CD163-positive macrophages that were negative for S100 protein and CD1a. Lymphocytes were mostly CD3, CD4-positive lymphocytes that were negative for cytotoxic markers, TIA-1 and granzyme-B. Polymerase chain reaction did not show B cell or T cell rearrangement. In situ studies for Epstein-Barr-encoded receptor were negative, as was ALK-1 immunohistochemistry. Major histocompatibility complex-1 and weak IgG4 were focally positive in skeletal muscle. Cases with severe inflammation had increased numbers of CD20-positive B cells and CD123-positive plasmacytic dendritic cells. S100 was strongest in skeletal muscle fibers with vacuolar change. Clinical diagnostic considerations ranged from benign entities such as rhabdomyoma, intramuscular lipoma, fibromatosis, myositis ossificans, proliferative myositis, inflammatory myofibroblastic tumor, and inflammatory myopathy to malignant entities such as rhabdomyosarcoma, leiomyosarcoma, liposarcoma, and lymphoma. Available follow-up revealed spontaneous regression.

CONCLUSIONS

Focal myositis occurs in specific muscle groups of young adults of both sexes without significant trauma. It is a largely unrecognized entity with specific histology including myopathic, focal neurogenic, fibrosis, and inflammatory features. It can be easily mistaken for an inflammatory myopathy, dystrophy, alternate reactive, or even neoplastic process. Focal myositis seems to be a macrophage and T-cell-rich lesion that changes to B cell and dendritic plasmacytoid cells when markedly inflamed, but does not seem to have a known viral or molecular etiology. IgG4 presence may be linked to the fibrosis in these lesions; a possible transient autoimmune etiology cannot be excluded. Careful attention to reproducible clinicopathologic features can aid diagnosis and spare patients from excessive surgery or adverse therapy.

MR imaging findings of focal myositis: a pseudotumour that may mimic muscle neoplasm

OBJECTIVE

The authors describe magnetic resonance (MR) findings in eight patients with histologically confirmed focal myositis.

MATERIALS AND METHODS

In each patient, axial TSE T1-weighted and fast short-tau inversion recovery (STIR) images were obtained using a 1.5-T MR scanner. Three patients also underwent dynamic contrast-enhanced MR examination using a GE T1-weighted sequence. The following features were evaluated: anatomical distribution, extent of the involvement, signal intensity characteristics, dynamic enhancement pattern and outcome at follow-up examinations.

RESULTS

Seven of eight lesions were located in the lower extremities, one of eight in the arm; four of eight involved part of a muscle, two of eight diffusely involved a muscle and two of eight showed multifocal involvement of two or more muscles. All lesions were hyperintense on fast-STIR images: the hyperintensity was homogeneous in six of eight and inhomogeneous in two of eight. On T1-weighted unenhanced images, all lesions but two appeared isointense or slightly hypointense in comparison to normal muscles; two lesions showed a slight hyperintensity. Dynamic enhancement pattern corresponded to the type usually seen in benign soft tissue lesions. All lesions disappeared.

CONCLUSION

Focal myositis is an uncommon pseudotumour which should be considered in the differential diagnosis of muscular masses and myopathies.

A muscular lesion suggestive of focal myositis in a child with Proteus syndrome

Proteus syndrome is a polymorphic hamartomatous disorder associated with a broad spectrum of rare congenital malformations. Many neoplasms have been linked to this condition, including lipomas, lymphangiomas, and hemangiomas. The authors describe a case of a congenital muscular lesion in a child with Proteus syndrome. This mass was painless but was growing out of proportion to her leg musculature. A magnetic resonance imaging scan and incisional biopsy showed findings consistent with focal myositis. The clinical, radiographic, and histologic characteristics of this previously undescribed lesion are discussed, with a brief review of the literature.

Overview of the radiology of connective tissue disorders in children

This review article describes the imaging finding of the connective tissue disorders in children. The radiological features of the following conditions are described; the spondyloarthropathics, systemic lupus erythematosus (SLE), dermatomyositis, scleroderma, the vasculitides, Kawasaki disease, synovitis, acne, pustulosis, hyperostosis, osteitis (SAPHO), and focal myositis. The features on several integrated imaging techniques are described.

Focal, steroid responsive myositis causing dropped head syndrome

The dropped head syndrome, which occurs in a variety of neuromuscular disorders, is usually not due to an inflammatory process and generally either self-limited or nonresponsive to therapy. We present an 80-year-old woman who developed progressive neck weakness over a few months due to a focal and restricted inflammatory process involving the neck extensor muscles. She responded dramatically to treatment with immunosuppressive therapy.

Focal myositis: a polymerase chain reaction analysis for a viral etiology

Focal myositis (FM) is a benign inflammatory condition that may clinically simulate a soft tissue sarcoma. It was first described in 1977, and only approximately 30 cases have been reported to date, yet this entity is probably more frequent. The pathogenesis of FM is totally unknown. It has been proposed that it represents a nodular form of myositis, which can evolve into polymyositis, but this hypothesis has not been confirmed by follow-up studies. We describe seven cases of FM, five of which have never been reported before. Histology of the lesions was very similar, showing a destructive inflammatory myopathy with evidence of regeneration. Our study attempted to better understand the pathogenesis of this focal inflammatory myopathy. We performed a polymerase chain reaction study to explore the presence of a number of viral infectious agents in the inflammed tissue. The present study failed to show the presence of a known viral agent with a recognized tropism for myofibers. With a panel of lymphoid cell markers, we also characterized the phenotype of the inflammatory infiltrate that was composed of many T-lymphocytes with few CD4+ cells. Lastly, we reviewed the published cases and discuss the possible pathogenesis.

Focal myositis presenting as pseudothrombophlebitis of the neck in a patient with mixed connective tissue disease

This report describes a case of focal myositis in a patient with mixed connective tissue disease. The patient presented with diffuse neck swelling and pseudothrombophlebitis of the left internal jugular vein. Other clinical features included a high fever, elevated erythrocyte sedimentation rate, and prompt improvement after administration of high-dose intravenous corticosteroid therapy. Criteria for polymyositis were absent, serum levels of creatine kinase remained normal, and there was no sign of recurrence during 3 years of followup. Results of immunoprecipitation for anti-Jo-1 and other myositis-specific autoantibodies remained negative in serial serum samples obtained before, during, and after the episode.

Focal myositis of the floor of mouth: report of two cases and review of the literature

Focal myositis is an uncommon inflammatory myopathy of unknown cause affecting skeletal muscle. It may be mistaken on clinical evaluation for a malignant neoplasm. We describe two cases, both involving the mylohyoid muscle of the floor of the mouth. In each case excisional biopsy of a firm indurated mass revealed a focal lymphocytic and histiocytic infiltrate associated with degenerating and regenerating skeletal muscle fibers. No clinical or biochemical evidence of generalized muscle disease was seen at presentation or at 1-year and 7-year follow-up examination. The literature on focal myositis involving the head and neck region is reviewed.

Focal myositis: a clinicopathological study

Focal myositis is a rare, benign inflammatory condition that may clinically simulate a soft tissue sarcoma. It was first described in 1977 and around 30 cases have been reported to date. We report two further cases on which we have performed immunocytochemistry and electron microscopy. Histology of both lesions was identical, showing a destructive inflammatory myopathy with evidence of regeneration. Stains for micro-organisms were negative and no viral particles were seen on electron microscopy. The immunocytochemical profile of our two cases differed from that of polymyositis: with a panel of T- and B-cell markers the cellular infiltrate was found to be composed of T-lymphocytes and variable numbers of macrophages: sub-typing in one case revealed the T-cells to be predominantly CD4+ cells. Use of antibodies to MHC class 1 and 2 antigens showed occasional positive inflammatory cells only. Clinicopathological correlations and the differential diagnosis are discussed.