Images in ID-What's the Diagnosis
Despite modern surgical techniques and advanced antimicrobial therapy, osteomyelitis remains a difficult and challenging problem.1,2 In adults, osteomyelitis is usually a subacute or chronic infection that develops secondary to an open injury to bone and surrounding soft tissue.3 We report an unusual case of a patient who developed chronic osteomyelitis due to inner table sequestrum 1 year after the management of sickle injury.
A 23-year-old woman had alleged history of assault with a sickle 2 years back on her left temporoparietal region. Skull radiograph and computed tomographic (CT) scan showed fracture of left parietal bone and no intracranial lesion (Fig. 1). At that time, she had no deficits; wound was sutured primarily without removing the bone fragments, and patient was managed with daily dressing and a course of oral antibiotics that was given for a week at a peripheral hospital. Patient was apparently all right till 1 year back than when she started to have swelling and pain at the injured site. It was followed by pus discharge (pus culture showed Staphylococcus aureus sensitive to ceftriaxone, amikacin, and cloxacillin) that was persisting, despite a course of antibiotics. There was no history of fever, seizures, or altered sensorium. Now, the patient attends our outpatient clinic, and on local examination, she had unhealthy pus-discharging sinus at the anterior and lower end of previous scar associated with tender and boggy swelling. All blood investigations were normal except for low hemoglobin level (8.8 g/dL) and raised erythrocyte sedimentation rate (37 mm in first hour). Estimation of C-reactive protein could not be done. Her repeat radiograph showed sclerosed bone fragment with irregular lower margin suggestive of chronic osteomyelitis (Fig. 2). Plain and contrast CT scan showed inner table sequestrum on bone window with mild enhancement of dura mater (Figs. 2C, 3). She was continued with the antibiotics (injectable ceftriaxone, 1 g IV every 12 hours; injectable amikacin, 500 mg IV every 12 hours for 1 week) according to the previous pus culture report, followed by oral cloxacillin 250 mg TID for additional 4 weeks. She underwent removal of loose fragment and unhealthy granulation tissue and debridement of surrounding unhealthy bone. Pus culture was sterile, and histopathology was suggestive of chronic inflammation and chronic osteomyelitis. At follow-up, the patient has not had any further complications after her most recent treatment.
As in the present case, the radiographs in chronic osteomyelitis may reveal osteolysis, periosteal reaction, and sequestra (segments of necrotic bone separated from living bone by granulation tissue).4,5 Plain films should always be the first step in the imaging assessment of osteomyelitis; however, the sensitivity for radiography has been reported to range from 43% to 75%, and the specificity, from 75% to 83%. The sensitivity and specificity of CT for the diagnosis of osteomyelitis are in the range of 65% to 75%; the sensitivity of magnetic resonance imaging for osteomyelitis has been generally reported as being between 82% and 100%, and specificity, between 75% and 96%.6 Computed tomographic scan will be helpful in detecting small areas of osteolysis in cortical bone, small foci of gas, and minute foreign bodies.4,7 In this case, CT scan showed a small piece of inner table that was acting as a sequestrum, and it also showed enhancement of dura, suggestive of chronic inflammation and infective foci. Because of the presence of infected bone fragments without a blood supply (sequestra), cure of chronic osteomyelitis with antibiotic therapy alone is rarely, if ever, possible in such cases.3,8 This patient had similar problem and have chronic discharging sinus for the last 1 year, with chronic purulent discharge. Adequate surgical debridement is the cornerstone of therapy for chronic osteomyelitis, and cure is not possible without removal of all the infected bone.3,8 Surgical debridement in patients with chronic osteomyelitis can be technically demanding.9 It is possible that with the retained fragment and drainage, there is localized osteomyelitis on nearby bone, and histopathology of surrounding bone will show the evidence and completeness of infection, although we could not perform such detailed examination in the present case. Histopathologic and microbiological examination of bone is the gold standard for diagnosing osteomyelitis. Cultures of sinus tract samples are not reliable for identifying causative organisms. Therefore, biopsy is advocated to determine the etiology of osteomyelitis.7,8 In this patient, pus culture was sterile maybe because she received a course of antibiotics; however, histopathology revealed features of chronic inflammation both in soft tissue and in the bone also. This case demonstrates the need for high index of suspicion and careful examination of the images and the need for adequate surgical control of infection in these patients.
The authors thank Ms Jayashree PR who assisted in writing and editing and offered suggestions for improvement of this paper.
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