Journal of Autoimmune Disorders

Keywords

Myositis ossificans; Heterotopic; Calcification; Scanner; Africa

Introduction

Myositis ossificans (MO) is a heterotopic ossification characterized by the occurrence of bone formation in a soft tissue, usually muscular. It can be hereditary or not [1,2]. Classic hereditary form (myositis ossificans progressiva) is caused by a recurrent activating mutation (617G>A; R206H) in the gene ACVR1/ALK2 encoding Activin A receptor type I/Activin-like kinase 2, a bone morphogenetic protein (BMP) type I receptor [3,4]. Thus, the developpement of small molecule ALK2 inhibitors to suppress BMP signaling will represent an effective treatment for myositis ossificans progressiva [5-7]. Non-hereditary forms are usually posttraumatic and well-trauma there occurs a tissue necrosis or bleeding initiating an uncontrolled vascular and fibroblastic activity resulting with bone formation [10,11]. Factors associated with development of MO traumatica include the severity of a contusion, continuing exercise after injury, massaging the injured area, applying local heat, and head injury [12]. Clinical signs are not specific and imaging haves a key role in diagnosis [13]. The diagnosis of MO can be confirmed by histology [2,14].circumscribed lesion that frequently complicates hematoma formation of the muscles, particularly of the proximal extremities [8,9]. It is believed that after a distinguishable trauma there occurs a tissue necrosis or bleeding initiating an uncontrolled vascular and fibroblastic activity resulting with bone formation [10,11]. Factors associated with development of MO traumatica include the severity of a contusion, continuing exercise after injury, massaging the injured area, applying local heat, and head injury [12]. Clinical signs are not specific and imaging haves a key role in diagnosis [13]. The diagnosis of MO can be confirmed by histology [2,14].

We report the case of a particular form of non-traumatic MO in a West African woman.

Case Report

A 55-year-old female with no particular family history or trauma has consulted for pain and swelling of the thighs evolving for two years. Walking and seating were gradually limited. There was no peripheral joint pain, and no general condition. Physical examination revealed a tumefaction of the thighs predominating right and induration zones on the middle third of the thighs. There was hypochromic microcytic anemia at 11.2 g/dl and the erythrocyte sedimentation rate was 97 mm at the first hour. X-ray (Figure 1) and CT scan (Figure 2) of the thighs showed massive ossifications of soft tissues, spanning the right hip. A muscle biopsy noted a focus of calcification within a fibro-adipose tissue (Figure 3). The patient was given analgesics and corticosteroids, which led to a modest regression of pain. Surgery was not considered because of the extended nature of ossification.

Figure 1: X-ray of the right thigh showing a large calcifications of soft tissues.

Figure 2: Computed tomography of the thighs: diffuse muscular ossification of the thighs and the right hip (reconstruction in 3D on the right and bone reconstruction on the left).

Figure 3: Muscle biopsy: calcification focus within fibro-adipose tissue.

Discussion

MO is a rare non-neoplastic condition characterized by heterotopic ossification of soft tissues. Myositis ossificans progressiva occurs at an earlier age and some cases have been described in sub-Saharan Africa [15-17]. Although trauma is found in 60 to 75% of cases [8], there are also non-traumatic forms such as the case of our patient. MO non-traumatica can be seen at any age and the lesion is often well circumscribed [11,18-21]. Localization of MO on thighs and hips is frequent and increases with age [22-25]. The case of our patient is rare because, the ossification is bilateral and involves several muscles. This situation did not allow us to consider surgery, which is useful in some circumscribed forms [19,20,25,26]. Clinical symptomatology (joint swelling and stiffness, nodules) may simulate rheumatoid arthritis [27] or ankylosing spondylitis [28] in some cases. Imaging is the key to diagnosis. Ultrasonography and Magnetic Resonance Imaging are useful in the acute phase of symptomatology even before the appearance of calcifications [13,24]. CT scan with 3D reconstruction shows better the ossification as it was seen for our patient [29]. The histology varies according to the degree of cellular maturation, but it can sometimes (at the early stage) be misleading and simulate an osteosarcoma [14,30]. In this case the lesion is extremely painful with a high level of alkaline phosphatase and there is no well-circumscribed appearance of the former on histopathology.

Conclusion

Myositis ossificans is a self-limiting, benign ossifying lesion that can affect any type of soft tissue. Diagnosis is based on clinical and imaging, and should be done early to limit the often associated functional disability.

Conflict of Interest

Nil.

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