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Pediatrics: General Medicine > Rheumatology
Myositis Ossificans
Article Last Updated: Jul 17, 2006
AUTHOR AND EDITOR INFORMATION
Section 1 of 10  
Author: Donald A Person, MD, Medical Director, Senior Scientist, Department of Clinical Investigation, Tripler Army Medical Center, Honolulu; Professor of Pediatrics, F Edward Herbert School of Medicine, USUHS, John A Burns School of Medicine, University of Hawaii at Manoa
Donald A Person is a member of the following medical societies: Ambulatory Pediatric Association, American Academy of Pediatrics, American College of Rheumatology, American Medical Association, American Pediatric Society, American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Association of Military Surgeons of the US, Clinical Immunology Society, Federation of American Societies for Experimental Biology, Pediatric Infectious Diseases Society, and Society for Pediatric Research
Coauthor(s):
Mandar A Pattekar, MD, MS, Consulting Staff, Department of Radiology, Methodist Hospital
Editors: Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine.com, Inc; David D Sherry, MD, Professor of Pediatrics, Division of Rheumatology, University of Pennsylvania; Director of Clinical Rheumatology, Children's Hospital of Philadelphia; Daniel Rauch, MD, FAAP, Director, Pediatric Hospitalist Program, Associate Professor, Department of Pediatrics, New York University School of Medicine; Barry L Myones, MD, Associate Professor, Departments of Pediatrics and Immunology, Pediatric Rheumatology Section, Baylor College of Medicine; Director of Research, Pediatric Rheumatology Center, Texas Children's Hospital
Author and Editor Disclosure
Synonyms and related keywords:
myositis ossificans, fibrodysplasia ossificans progressiva (hereditary type), myositis ossificans circumscripta, myositis ossificans progressiva, soft tissue ossification, progressive ossifying myositis, myositis ossificans traumatica, heterotopic osteogenesis, progressive osseous heteroplasia
Background
Myositis ossificans is a misnomer and the term fibrodysplasia ossificans progressiva (FOP), as used by McKusick, is preferred. It is a rare autosomal dominant disorder characterized by skeletal malformation and progressive, disabling heterotopic osteogenesis. The condition was first described by Guy Patin in 1692.
Pathophysiology
Myositis ossificans manifests in 2 forms.
Myositis ossificans circumscripta can develop either in response to soft tissue injury (eg, blunt trauma, stab wound, fracture/dislocation, surgical incision) or can occur without known injury. Proposed mechanisms for atraumatic myositis ossificans include nondocumented trauma, repeated small mechanical injuries, and nonmechanical injuries caused by ischemia or inflammation.
Recently Shore et al reported mapping FOP to chromosome 2q23-24 by linkage analysis. They have further identified an identical heterozygous mutation (617G®R206H) in the glycine-serine (GS) domain of the activin A receptor type I (ACVR1) gene, a bone morphogenic protein (BMP) type I receptor in all affected individuals thus far examined.
Frequency
International
A recent report suggested the incidence of FOP to be less than 1 in 10-7.
Race
Myositis ossificans progressiva occurs in all races.
Sex
Myositis ossificans progressiva demonstrates no definitive sexual predilection because the slight male predominance overall probably relates to differences in physical activity levels between the genders.
Age
- Nonhereditary myositis ossificans is uncommon in children; fewer than 6.7% of cases occur in the first decade of life.
- In FOP, average age of onset is 5 years, with a reported onset range from fetus to 25 years.
History
- Nonhereditary myositis ossificans
- Pain, tenderness, focal swelling, and joint/muscle contractions occur.
- The condition can be asymptomatic and may be diagnosed incidentally.
- The history of trauma causing the condition may be difficult to elicit.
- Most (ie, 80%) ossifications arise in the thigh or arm. Other sites include intercostal spaces, erector spinae, pectoralis muscles, glutei, and the chest wall.
- FOP
- The condition produces painful lumps and stiffness in the adjoining joint. Lumps decrease in a few weeks, but joint mobility reduction persists.
- Exacerbating factors for ossifications at new sites includes sometimes very minor trauma, such as venipuncture, biopsy of lumps, IM injections, dental treatments, and excision of masses.
- The most common sites are the sternocleidomastoid muscle, paraspinal muscles, the masticatory muscles, and shoulder and pelvic girdle muscles. Spared are the abdominal muscles, extraocular muscles, and GI tract and tongue muscles.
- Ossification progresses from proximal to distal and cranial to caudal.
Physical
- Myositis ossificans circumscripta
- Tender mass, with or without cutaneous erythema
- Associated joint motion abnormalities
- Fever (uncommon)
- FOP
- Digits: Short hallux with synostosis and, less often, short thumbs
- Fibrous Tissues: Swelling (sometimes with pain and fever) in aponeuroses, fasciae, and tendons, which leads to ossification in muscles and fibrous tissues, most prominent in the neck dorsal trunk and proximal extremities (The sternocleidomastoid muscle is commonly affected.)
- Kyphoscoliosis: Restricted shoulder and pelvic girdle movements
Osteosarcoma
Other Problems to be Considered
Myositis ossificans progressiva Weber-Christian disease
Klippel-Feil syndrome
Rheumatoid arthritis
Dermatomyositis of childhood
Systemic sclerosis
Calcinosis interstitialis ossificans
Albright hereditary osteodystrophy
Pseudohypoparathyroidism
Lab Studies
- Routine laboratory results are generally within the reference range. Erythrocyte sedimentation (ESR) and white WBC count are usually normal.
- In myositis ossificans progressiva, ECG findings may be abnormal, while spirometry may demonstrate a restrictive pattern, reflective of chest wall involvement.
Imaging Studies
- Plain radiography of nonhereditary myositis ossificans circumscripta
- Early examination may be unremarkable.
- Floccular calcified density is observable in soft tissues at 2-6 weeks from onset.
- By 6-8 weeks, calcification becomes sharply circumscribed.
- Ossifications tend to adhere to the periosteum.
- Obtain serial radiographs to distinguish between myositis ossificans and osteogenic sarcoma. In osteogenic sarcoma, calcification extends centrifugally to periphery. In myositis ossificans, calcification first occurs in the periphery of the soft tissue mass (centripetally). Myositis ossificans' calcification occurs in association with the bone's diaphysis, unlike osteogenic sarcoma, where calcification is associated with the metaphysis.
- Plain radiography of FOP
- Short metacarpals and metatarsals
- Phalangeal synostosis (eg, monophalangeal great toe)
- Vertebral fusions, vertebral anomalies (ie, small bodies), pedicle thickening
- Thick, short femoral neck
- Variations in bone maturation sequence
- Increased incidence of enchondromas
- The CT scan demonstrates fascial plane edema and swelling, even before ossification has occurred.
- MRI findings depend on the age of the lesion.
- In immature lesions, T2-weighted spin-echo images are associated with a homogeneous soft tissue mass with increased signal intensity. Surrounding edema may be seen in lesions less than a few months old. In T1-weighted images, only mass effect may be noted with displacement of fascial planes.
- Mature lesions appear as inhomogeneous masses with fatlike signal intensity on both T1- and T2-weighted images.
- Bone scintigraphy reveals enhanced uptake in immature lesions. Once maturation occurs, uptake becomes comparable with normal bones.
- Ultrasonographic examination shows echogenic and shadowing mass.
Procedures
- Once diagnosis is established, usually clinically, any surgical biopsy is contraindicated in FOP.
- In nonhereditary myositis ossificans, perform a biopsy primarily to exclude osteogenic sarcoma.
Histologic Findings
Ossification has 3 distinct zones: the central undifferentiated zone, the surrounding zone of immature osteoid formation, and the peripheral zone with mature bone. At least 10 days are required following onset of symptoms for these zones to become apparent. If the biopsy is performed before 10 days have elapsed, or if a biopsy sample is obtained from the central region, the specimen yields undifferentiated tissue resembling an osteosarcoma.
In contrast to osteogenic sarcoma, myositis ossificans exhibits a zonal pattern, the lesion has viable muscle fibers, and the process does not invade surrounding tissue.
Biopsy performed after ossification maturation reveals primarily mature lamellar bone. Biopsy of lesions from patients with myositis ossificans atraumatica may lack the typical histological appearance of myositis ossificans.
Medical Care
No established medical therapy exists. Pain medications may be indicated, as well as other supportive measures, such as gentle occupational and/or physical therapy.
Surgical Care
Surgical care is warranted in patients with nonhereditary myositis ossificans only after maturation of the lesion (6-24 mo). Life-saving surgery, particularly abdominal surgery, is apparently tolerated by patients with FOP.
Activity
Numerous reports of catastrophic falls in patients with FOP have been noted. Nearly twice as many patients with FOP suffer serious injury with falls as compared to controls.
Deterrence/Prevention
- Patients with mild features of myositis ossificans progressiva can reproduce; their offspring have a 50% probability of inheriting the condition.
Prognosis
- The outcome for patients with nonhereditary myositis ossificans includes the following:
- Possible spontaneous resorption
- Typical lesions that decrease in size and persist
- Patients with myositis ossificans progressiva experience progressive ossification.
Medical/Legal Pitfalls
- Myositis ossificans can occur as a complication of fractures, especially in supracondylar fractures of the humerus. Ossification is associated with
high-energy trauma, manipulation, surgical intervention, aggressive-passive range-of-motion exercises, or associated head injury. Myositis ossificans, however, can occur without any of these factors. - Myositis ossificans and osteogenic sarcoma may be difficult to differentiate. A rare situation also occurs of malignant transformation of the ossified region.
| Media file 1:
Bilateral monophalangeal great toe. Image contributed by Ajay K. Singh, MD, William Beaumont Hospital, Royal Oak, Mich. |
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| Media file 2:
Lateral view of the neck showing calcification in the paraspinal muscles. Image contributed by Ajay K. Singh, MD, William Beaumont Hospital, Royal Oak, Mich. |
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Media type: X-RAY
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| Media file 3:
Anteroposterior view of thoracolumbar spine showing massive calcification of paraspinal muscles. Image contributed by Ajay K. Singh, MD, William Beaumont Hospital, Royal Oak, Mich. |
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Media type: X-RAY
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| Media file 4:
Lateral view of the same patient as in Image 3. Note the loss of normal spinal curvature. Image contributed by Ajay K. Singh, MD, William Beaumont Hospital, Royal Oak, Mich. |
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Media type: X-RAY
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| Media file 5:
Nine-year-old Mexican girl with Fibrodysplasia Ossificans Progressiva (FOP). |
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Media type: Image
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| Media file 6:
Technetium 99-Tc scan of the spine of the nine-year-old girl in Image 5. |
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Media type: X-RAY
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| Media file 7:
Spine and pelvis radiograph of the nine-year-old girl in Images 5 and 6. |
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Media type: X-RAY
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Myositis Ossificans excerpt Article Last Updated: Jul 17, 2006
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