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TRAUMATIC MYOSITIS OSSIFICANS SIMULATING SOFT TISSUE INFECTION

1996; Lippincott Williams & Wilkins; Volume: 15; Issue: 6 Linguagem: Inglês

10.1097/00006454-199606000-00020

1532-0987

Elisabeth E. Adderson, John F. Bohnsack,

Soft tissue tumor case studies

Traumatic myositis ossificans (TMO) is a benign disorder of heterotopic bone formation occurring in response to soft tissue trauma. It most commonly presents in young adults and children as a painful, enlarging mass of the arm or thigh. There is frequently no significant history of injury and the lesion may be mistaken for a malignant tumor of bone or soft tissue. We report an adolescent in whom TMO presented with systemic and local signs and symptoms suggestive of a rapidly progressive soft tissue infection late during her hospitalization for multiple injuries. Case report. A previously healthy 13-year-old girl was admitted to our Intensive Care Unit in June, 1995, after a motor vehicle accident in which she was an unrestrained passenger. She sustained multiple facial fractures and a right temporal skull fracture. On admission radiographs of all extremities were normal. A computerized tomography scan of the abdomen suggested a pancreatic transection, but an exploratory laparotomy did not reveal significant intraabdominal injuries. Severe pulmonary contusions and acute respiratory distress syndrome necessitated mechanical ventilation and the use of inhaled nitric oxide. Her hospital course was complicated by the development of multiple pneumatoceles, pneumothoraces and pneumopericardium which were treated by high frequency oscillatory ventilation and chronic chest tube drainage. On the eighth hospital day she developed fever, leukocytosis and hypotension. Blood, urine and cerebrospinal fluid cultures were sterile and a bronchoalveolar lavage grew Acinetobacter calcoaceticus, Enterobacter cloacae and Candida albicans. She was treated with a 4-week course of piperacillin-tazobactam, gentamicin and fluconazole with progressive improvement in her respiratory condition. Four days after antibiotics were discontinued (Hospital Day 43) the patient's sedation and paralysis were weaned and she complained of severe pain of her knees and right shoulder. During the next 36 h she developed erythema, warmth and swelling above both knees, which progressed caudally to involve both thighs and the left inguinal region. A fever of 39.4°C was noted. Physical examination demonstrated bilateral knee effusions, induration and extreme tenderness to palpation of the quadriceps bilaterally and a firm, ill-defined, slightly mobile, 4- by 6-cm mass above the right knee. Arterial pulses were palpable in both lower extremities and venous pulsations were present bilaterally by doppler examination. The white blood cell count was 19 000/mm3, with 20% band forms and 40% polymorphonuclear leukocytes. An erythrocyte sedimentation rate was 119 mm/h. Aspiration of the right knee yielded 10 ml of serous fluid with a white blood cell count of 660/mm3 (90% lymphocytes, 5% polymorphonuclear leukocytes), a red blood cell count of 2.65 × 105/mm3, glucose 108 mg/dl and protein 4 000 mg/dl. Blood and urine cultures were obtained and therapy with nafcillin and ceftazidime was begun. A computed tomographic scan of the lower extremities demonstrated soft tissue swelling overlying both femurs. Concentric areas of low attenuation with peripheral calcification were present in the soft tissue. The appearance was thought to be typical of myositis ossificans. A third calcified mass was present in the left psoas muscle overlying the left femoral neck (Fig. 1). Marked edema of adjacent soft tissues, consistent with inflammation, and bilateral knee effusions were also present but no contrast enhancement was noted. A plain radiograph of the right shoulder also demonstrated early heterotopic calcification overlying the joint. Antibiotics were discontinued after 72 h and a passive range of motion exercises, ibuprofen and etidronate disodium therapy were begun. The patient remained febrile with a mild leukocytosis for 3 weeks after the onset of symptoms; however, repeated cultures of blood and urine were sterile during this period and the erythema and swelling of her legs gradually resolved. Epidural bupivicaine and fentanyl and intravenous or oral narcotic analgesics were needed to control pain and permit continued physical therapy. The patient was discharged to a rehabilitation facility on the 75th day of hospitalization. At that time she had no major pulmonary or neurologic sequelae but continued to have marked limitation of mobility because of severe leg pain and ankylosis of the left hip. Discussion. Two distinct forms of myositis ossificans have been described. Myositis progressiva is a rare genetic disorder characterized by widespread progressive soft tissue calcification and hypoplasia of the phalanges, first metacarpals and first metatarsals.1 Most myositis ossificans, however, follows musculoskeletal or generalized trauma. Sixty to 75% of cases of myositis ossificans follow an injury (or repeated injury) of an extremity, most commonly the upper arm or quadriceps. The mechanism responsible for heterotopic bone is not known, but it is associated with proliferative repair processes. TMO has developed during the course of tetanus and polio.2 Two to 3% of patients with severe burn injuries develop myositis ossificans, as do a small proportion of patients with paraplegia and 3 to 20% of patients with severe head injuries.1, 3, 4 About 25% of otherwise healthy patients with TMO do not recall significant antecedent trauma. Traumatic myositis ossificans typically presents with pain and an enlarging mass in the affected soft tissue (pseudomalignancy). Marked warmth, edema and restricted range of motion are common features, although occasionally patients may present with minimal pain or with flexion contractures. Fever is common and may be prolonged, suggesting osteomyelitis.5 An elevated erythrocyte sedimentation rate typically persists throughout the inflammatory phase of the illness.6 Knee effusions are noted in 30% of TMO complicating severe quadriceps contusions.6 Histologic examination of TMO within the first few days after injury demonstrates proliferation of primitive mesenchymal cells which may mimic a soft tissue sarcoma. The mature lesion has a characteristic zone appearance with a central region of proliferative fibroblasts and undifferentiated connective tissue and an intermediate layer of immature osteoid formation. The peripheral portion consists of more mature fibrous stroma which begins to ossify between 10 days and 4 weeks after injury, ultimately forming cancellous bone.1, 7 The diagnosis of TMO may be made by radiologic or pathologic examination. Early imaging of affected muscle may demonstrate a soft tissue mass. By 4 weeks diffuse peripheral calcification (the “dotted veil appearance”) is present and by 5 to 6 months after injury mature bone is readily apparent on plain radiographs.7 Periosteal reaction of adjacent bone is common, but bony destruction is more suggestive of a malignant process. Computerized tomography scanning is a highly sensitive technique for detection of early peripheral calcification and the characteristic lucency separating heterotopic bone from adjacent skeletal structures. Magnetic resonance imaging and technetium or gallium radionucleotide scans are less helpful in distinguish TMO from malignant or infectious lesions. Bone scans may be useful, however, in following the osteoblastic activity and maturation of lesions. The incidence of TMO may be reduced by the prompt identification of significant muscle injury and early institution of immobilization, followed by progressive range-of-motion exercises.2, 6, 8 Etidronate disodium blocks the aggregation, growth and mineralization of calcium hydoxyapatite crystals and other osseous precursors and has been effective in decreasing the frequency of heterotopic ossification after head injury and hip replacement.9 The best therapy for established TMO is not clear. Nonsteroidal antiinflammatory agents are usually prescribed. Early surgical therapy may exacerbate the formation of heterotopic bone and prolong recovery, as may reinjury of involved tissues. The majority of minor lesions are self-limited, with pain and limitation of motion lasting less than 1 month and partial or complete resorption of heterotopic bone in about 35% of cases.1, 6 Myositis ossificans associated with severe injuries, however, may cause prolonged disability similar to that experienced by our patient. Those patients reported by Jackson and Feagin6 with TMO complicating moderate or severe quadriceps contusions had a duration of functional impairment ranging from 45 to 180 days. Indications for late surgical therapy include involvement of the origin or insertion of a muscle or tendon, or the persistence of large masses causing significant pain or loss of function. We presume our patient had quadriceps injury that was not clinically obvious at the time of her admission to the hospital. She also had a second risk factor for TMO, severe head injury, which may have increased the possibility of this complication. Symptoms of TMO typically develop 4 to 6 weeks after injury. While our patient became symptomatic relatively late, her prolonged sedation and analgesia may have delayed recognition of early symptoms. TMO is uncommon in acute care settings, and the rapid progression of our patient's clinical signs, her systemic symptoms and her high risk of nosocomial infection led us to postulate an infectious process as the most likely etiology for our patient's illness. The diagnosis of TMO was not entertained until diagnostic imaging was performed. TMO should be considered in the differential diagnosis of inflammatory disorders of bone and soft tissue, particularly after documented trauma. Increased awareness of the risk factors for TMO in injured patients may facilitate the early institution of prophylaxis and therapy, minimizing later disability. Elisabeth E. Adderson, M.D.; John F. Bohnsack, M.D. Department of Pediatrics University of Utah School of Medicine Salt Lake City, UTFIG. 1: Computed tomographic scan of the thighs demonstrating a large soft tissue mass with peripheral calicification and surrounding soft tissue swelling in the left psoas muscle.