Ann Thorac Surg 2002;73:1296-1298
© 2002 The Society of Thoracic Surgeons
Case report
Proliferative myositis: a rare pseudosarcoma of the chest wall
Michael S. Kent, MDa,
Douglas B. Flieder, MDa,
Jeffrey L. Port, MDa,
Nasser K. Altorki, MD*a
a Departments of Cardiothoracic Surgery and Pathology, The New York-Presbyterian Hospital, Weill-Cornell Medical Center, New York, New York, USA
Accepted for publication August 14, 2001.
* Address reprint requests to Dr Altorki, Department of Cardiothoracic Surgery, The New York-Presbyterian Hospital, Suite F22, 525 East 68th St, New York, NY 10021 USA
e-mail: nkaltork{at}mail.med.cornell.edu
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Abstract
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Proliferative myositis is a rare, inflammatory tumor that is often misdiagnosed as sarcoma. The clinical course of proliferative myositis is benign, and local recurrence after simple excision is uncommon. Typically, the lesion presents in the extremities or the head and neck. We present an unusual case of proliferative myositis with involvement of the anterior chest wall.
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Introduction
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Proliferative myositis (PM) is one of several benign tumors of the soft tissue. Its rapid growth and bizarre microscopic appearance often lead to the misdiagnosis of a high-grade sarcoma. Fortunately, recurrence even after subtotal excision is infrequent and therefore radical surgery is rarely required. We present an unusual case of PM affecting the chest wall and discuss the clinical and microscopic features of this uncommon tumor.
A 48-year-old man presented to the thoracic service for evaluation of a painful, rapidly enlarging chest wall mass. The tumor was in the left parasternal area and had increased in size during the past 4 weeks. A computed tomographic scan of the chest (Fig 1) demonstrated a 5-cm x 7-cm bulky mass involving the left pectoralis major muscle with extension into the sternum. An incisional biopsy revealed a benign, spindle-cell process involving the skeletal muscle, consistent with proliferative myositis. At operation, the mass was noted to erode into the lateral aspect of the sternum and the first three ribs. To obtain a complete resection, a partial sternal and rib resection was performed. The resulting defect was reconstructed with Marlex mesh (Meadox Medical Systems, Oakland, NJ) and methyl methacrylate. Soft tissue coverage was obtained with a pectoralis major rotational flap. Final pathologic examination confirmed the diagnosis of proliferative myositis. At 1-year follow-up the patient is well and free of recurrence.
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Fig 1. Computed tomographic scan demonstrating erosion of the mass into the sternum and pectoralis major.
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Comment
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Proliferative myositis is one of several benign, rapidly enlarging tumors of the soft tissue that are often confused with sarcoma. Although their rapid growth and often-bizarre microscopic appearance may suggest an aggressive course, these pseudosarcomas are clinically benign and rarely recur after subtotal excision.
The term pseudosarcoma encompasses three benign tumors of the soft tissue: nodular fasciitis, PM, and proliferative fasciitis. Of the three, PM is the least common, with fewer than 100 cases reported in the English-language literature. The first three cases were presented in abstract form by Ackerman in 1958 [1]. The disease was subsequently named by Kern, who reported seven cases in 1960 [2]. Enzinger and Dulcey reported the largest series of 33 cases in 1967 [3]. Although extremely rare, PM is an important clinical entity given its propensity for confusion with high-grade sarcoma.
The clinical presentation of PM is nonspecific. Adults are usually affected with a peak incidence between 40 and 70 years. Reports of cases in children are extremely uncommon. Most patients report a rapidly enlarging, soft tissue mass, usually affecting the shoulder girdle and upper extremity. Proliferative myositis may also involve the soft tissue of the head and neck. In the series of 33 cases reported by Enzinger and Dulcey [3], 18 involved the shoulder and arm whereas only 4 cases arose from the anterior chest wall. The mass often evolves over the course of a few weeks, and may double in size during several days. The lesion is usually 3 to 6 cm at presentation, and is typically firm and deep-seated.
Several microscopic features are characteristic of PM. First, a dense fibroblastic proliferation is noted to affect the epimysium, perimysium, and endomysium of the muscle bundles. This reaction is most pronounced in the septa surrounding the larger muscle fibers. Unlike sarcoma, PM rarely invades the surrounding muscle. On occasion, however, secondary muscle atrophy or focal ischemic necrosis may be observed. This alternation of proliferative connective tissue surrounding viable muscle fibers often gives rise to the so-called checkerboard effect, which is characteristic of the disease (Fig 2).
Secondly, a proliferation of bizarre, giant cells is often seen within this connective tissue matrix. These cells resemble ganglion cells or rhabdomyoblasts, and their presence often leads to the misdiagnosis of malignancy, such as ganglioneuroblastoma or rhabdomyosarcoma. However, the immunohistochemical profile of these cells (vimentin and actin positive and myoglobin negative) suggests a myofibroblastic origin. In addition, electron microscopy has demonstrated these cells to contain fine microfilaments and a prominent rough endoplasmic reticulum, also consistent with a myofibroblast lineage [4]. These cells are universally diploid on flow cytometry, lending further evidence to the belief that these cells are not malignant [5].
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Fig 2. Muscle fibers and surrounding connective tissue give rise to the "checkerboard effect" characteristic of proliferative myositis. (Hematoxylin & eosin x40.)
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The distinction between PM and other pseudosarcomas may be difficult even for the experienced pathologist. Microscopically, PM is indistinguishable from proliferative fasciitis. The latter, however, typically involves the subcutaneous tissue rather than the deeper muscle fascia [6]. Differentiation from nodular fasciitis is usually more straightforward. Nodular fasciitis often appears as a well-demarcated nodule that arises from the superficial fascia of the muscle [7]. Unlike PM, nodular fasciitis is common in children. Additionally, the microscopic appearance of nodular fasciitis is distinct, without the large, basophilic cells seen in PM.
Although the precise cause is unknown, PM is believed to be a reactive, inflammatory process. Approximately one third of patients will report a history of recent trauma to the affected area. Subclinical vascular injury may also be a precipitating event. Microscopic evidence of endarteritis has been observed in the lesions of some patients who have a history of thrombophlebitis and pulmonary embolism [7].
The prognosis for patients with PM is excellent. Although operation is often performed for diagnosis and removal of a cosmetically disfiguring mass, recurrence even after simple excision (ie, with positive microscopic margins) is extremely rare. Indeed, with a follow-up period of 1 to 16 years no recurrences were noted in the series reported by Enzinger and Dulcey [3]. However, among the 33 patients reported, 14 had been misdiagnosed as sarcoma and had undergone radical resection. In contrast to sarcoma, PM rarely invades normal tissue and can usually be readily excised. The erosion of the thoracic cage seen in this case is distinctly uncommon. Even with subtotal resection, PM is unlikely to recur. Consultation with an experienced pathologist after an incisional biopsy will confirm the benign nature of the disease. The majority of patients, therefore, can be spared radical resection if the diagnosis has been made with certainty.
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References
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Ackerman L.V. Extra-osseous localized non-neoplastic bone and cartilage formation (so-called myositis ossificans). J Bone Joint Surg Am 1958;40:279-298.[Abstract/Free Full Text]
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Kern W.H. Proliferative myositis: a pseudosarcomatous reaction to injury. Arch Pathol 1960;69:209-216.
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Enzinger F.M., Dulcey F. Proliferative myositis: report of thirty-three cases. Cancer 1967;29:2213-2223.
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Craver J.L., McDivitt R.W. Proliferative fasciitis: ultrastructural study of two cases. Arch Pathol Lab Med 1981;105:542-545.[Medline]
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el-Jabbour J.N., Wilson G.D., Bennett M.H., Burke M.M., Davey A.T., Eames K. Flow cytometric study of nodular fasciitis, proliferative fasciitis and proliferative myositis. Hum Pathol 1991;22:1146-1149.[Medline]
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Chung E.B., Enzinger F.M. Proliferative myositis. Cancer 1975;36:1450-1458.[Medline]
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Hutter R., Stewart W., Foote F. Fasciitis. A report of 70 cases with follow-up proving the benignity of the lesion. Cancer 1962;15:992-1003.
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Case 118: Proliferative Myositis
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Abstract
Introduction
