Clinical Radiology (2008) 63, 348e351
CASE REPORT
Childhood osteomyelitis presenting as a pathological fracture M.N. Taylorb, R. Chaudhurib, J. Davisb, V. Novellic, M.S. Jaswona,* Whittington Hospital NHS Trust, Departments of aPaediatrics, and bRadiology, London, UK, and c Great Ormond Street Hospital for Children NHS Trust, Host Defence Department, London, UK
Introduction Osteomyelitis in childhood is an important though relatively uncommon infection. The incidence is less than 1 in 10,000 pre-teenage children and the character of this condition has changed from that of a septicaemic illness to one where the pathology is confined to the skeletal system.1 The diagnosis of osteomyelitis before extensive infection has occurred is often difficult, yet early recognition is essential in order to treat and prevent permanent damage and disability. Correct diagnosis will also avoid confusion with other inflammatory or traumatic conditions affecting the skeletal system, including non-accidental injury (NAI). We present a case of a child with an atypical presentation of osteomyelitis. We review the literature, and discuss the role of various imaging methods, in particular, that of magnetic resonance imaging (MRI), in aiding diagnosis.
Case report A 7-month-old child was referred from the Emergency Department with a radiological diagnosis of a fracture of the left proximal humerus. The history given was that she had been reluctant to move her left arm since the morning of admission and screamed when the left arm was manipulated during changing. There was no history of trauma. A * Guarantor and correspondent: M. Jaswon, Whittington Hospital NHS Trust, Departments of Paediatrics and Radiology, Magdala Avenue, London N19 5NF, UK. Tel.: þ44 7699 705410; fax: þ44 207 288 5215. E-mail address:
[email protected] (M.S. Jaswon).
week earlier she was seen by her GP because of a febrile illness that settled following treatment with amoxicillin, although she remained somewhat miserable. On examination she was afebrile. Her general condition was satisfactory and her weight was on the 50th centile. She was unwilling to move her left arm, but there were no bruises, swelling or other signs of inflammation. The radiograph (Fig. 1) suggested a transverse fracture of the left proximal humerus, with a periosteal reaction estimated at being at least 7 days of age. No explanation was forthcoming as to how this injury may have occurred and the suspicion of non accidental injury (NAI) was raised. An aunt who was part of the family unit, had previously reported domestic violence. The skeletal survey performed was otherwise normal, as was an opthalmological examination. A strategy meeting was convened with the Children and Families (Social Services) Department. However, a radiograph taken 3 days later (Fig. 2) showed extensive permeative change at the site of the fracture in the humeral metaphysis suggesting that this was a pathological fracture. A full blood count showed a raised white count of 21.3 109/l (neutrophils 7 109/l with some atypical lymphocytes on the film), a haemoglobin of 10.6 g/dl, and a platelet count of 1035 109/l. The C-reactive protein (CRP) was raised at 27 mg/l (normal range 0e5 mg/l). An MRI examination (Fig. 3a, b) performed 7 days after the child’s presentation to the Emergency Department, showed a cortical break in the proximal metaphysis of the left humerus, associated with extensive bone marrow oedema, small sub-periosteal collections and a periosteal reaction along the shaft of the humerus, with involvement of the adjacent epiphysis. Soft-tissue swelling, a small shoulder
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Figure 1 Radiograph showing a fracture through the proximal left humerus (long arrow) and periosteal reaction along the shaft. There is also soft-tissue swelling around the shoulder joint (small arrows).
joint effusion, and multiple enlarged axillary and supra-clavicular lymph nodes were also noted. Together, these findings were concluded to be consistent with a diagnosis of osteomyelitits. The child underwent biopsy of the proximal humerus and microbiological culture grew Staphylococcus aureus. Her total white count remained raised and, although there was no significant neutrophilia, the neutrophils did show some toxic granulation. The platelet count continued to rise reaching a maximum of 3432 109/l. A central line was inserted and a 6-week course of intravenous flucloxacillin and oral fucidic acid was commenced. Whilst the platelet counts were above 1000 109/l, low-dose aspirin was administered. Following commencement of treatment, the white cell count, platelets, and inflammatory markers quickly settled, and normal function of the left shoulder was resumed. The senior social worker and consultant paediatrician
Figure 3 (a) T1W coronal MRI image of left humerus showing an upper metaphyseal fracture (long white arrow) with displacement through the epiphysis. There is abnormal low signal around the level of the fracture and in two abscess cavities within the medulla (short white arrows) as well as around the cortex. There is a marked periosteal reaction (black arrow). (b) Axial PD MRI image showing high signal in the intramedullary cavity (oedema or infected marrow; double-headed arrow), a cortical break (short black arrow) and periosteal elevation posteriorly (long black arrow). There is also extensive soft-tissue oedema (curved arrow) and there are enlarged axillary lymph nodes (white arrows).
met with the family to explain to them that it was now clear that the child had not been subjected to a deliberate injury.
Figure 2 Radiograph taken 2 days later showing extensive permeative change at the humeral metaphysis (long white arrow) with more established periosteal reaction and new bone formation (black arrow). There is lateral displacement of the humeral head. There is osteopaenia distally (curved arrow) indicating extension of pathological bone. Soft-tissue swelling again noted (small white arrows).
Discussion This case raises several points, including osteomyelitis presenting as a pathological fracture; the initial diagnosis of non-accidental injury; the usefulness of MRI as an imaging technique for the diagnosis of bony infection; and thrombocytosis as a marker of bony infection.
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The final diagnosis in this case was that of a pathological fracture secondary to bacterial osteomyelitis. The alternative, that this may have been a closed fracture with secondary infection, is most unlikely, as it is very rare in otherwise healthy and immunocompetent persons for infection to complicate a closed fracture.2 Indeed, in the medical literature, there are very few case reports of infection complicating a closed fracture.3e5 In 1978, a review of over 200 cases of acute haematogenous osteomyelitis in childhood highlighted the fact that none of the cases were secondary to infection of a closed fracture, despite the multiple abrasions and superficial trauma that these otherwise healthy children regularly sustained (Katz A., unpublished). The site of infection involving the metaphysis and adjacent epiphysis in this case is characteristic of osteomyelitis in infancy. In early childhood, vascular channels cross from the metaphysis into the epiphysis, acting as a pathway for the spread of infection into the epiphysis. This contrasts tumour growth, where the growth plate restricts disease extension much more effectively. Growth plate damage from infection may result in growth disturbances and deformity later in life. Also, as a result of this anatomical connection, primary osteomyelitis in infancy can present clinically as a ‘‘septic arthritis.’’6 From the age of 15 months, the transphyseal vessels close, and the infection remains localized to the metaphysis. The diagnosis of NAI is an important issue and should be carefully considered. The psychological and emotional trauma incurred by a family in which these allegations are made (albeit subsequently withdrawn), should not be underestimated. In this case, the Children and Families Department social worker, together with senior medical staff, met the family again to explain the situation and why it was found necessary to exclude NAI. MRI is currently the technique of choice in aiding the diagnosis of osteomyelitis. It is particularly helpful in distinguishing the causes of a pathological fracture in the early stages, and can help reduce the morbidity associated with a delayed diagnosis. MRI is able to distinguish septic arthritis, cellulitis, and non-inflammatory conditions from osteomyelitis more accurately than other imaging methods.7 It also delineates the extent of infection more accurately. The sensitivity and specificity of MRI for the detection of osteomyelitis is between 86e98 and 77e100%, respectively.8 Radiography, by comparison, may be normal for up to 14 days after the onset of symptoms, and although the specificity is high, the sensitivity in the early stages is low.
M.N. Taylor et al.
Bone scintigraphy is sensitive in the early stages of osteomyelitis, but specificity is limited and may yield false-negative results if the infection lies close to a growth plate, as it did in the present case, when the increased uptake associated with infection may be masked by the normal physiologically high uptake from the physis.9 Park et al. reviewed 100 consecutive children with acute extremity pain and found errors in the interpretation of triplephase bone scintigraphy, including simulation of infection by fracture, obscuration of osteomyelitis by a septic arthritis, prior antibiotic treatment, and cold defects due to ischaemia.10 Furthermore, due to its low spatial resolution, radionuclide bone scintigraphy may fail to distinguish soft-tissue infection from an osteomyelitis. Use of white cell scintigraphy, single photon emission computed tomography (SPECT) or positron emission tomography (PET) would increase the specificity and improve localization. Ultrasound has been used in the early diagnosis of osteomyelitis and detects periosteal changes, subperiosteal abscesses, and joint effusions, but the overall sensitivity for the detection of osteomyelitis by ultrasound, which is highly operatordependent, remains low.11 CT has a limited role, but may be a helpful adjunct to plain radiographs and bone scintigraphy.7 Its high spatial resolution makes it sensitive for the detection of foreign bodies, small sequestra, and small pockets of gas, but its specificity in differentiating active from chronic infection is low. MRI detects increased intra-medullary water and decreased fat content, which occurs when there is inflammatory exudate, oedema, hyperaemia, and ischaemia, all of which are markers of infection. These changes manifest as decreased T1-weighted (W) signal within the bone marrow, the inflammatory rim of which enhances after intravenous gadolinium injection, with a corresponding increase in signal on T2W, PD (proton density) and STIR (short tau inversion recovery) images. Other features of acute osteomyelitis on MRI, which were present in this case, include involvement of the epiphysis, a joint effusion (which may be reactive or indicative of a complicating septic arthritis), cortical breach manifest as focal or linear high T2W signal, periosteal new bone formation, and a subperiosteal collection demonstrated as a T2 hyperintense halo surrounding the cortex. MRI is also sensitive at detecting associated abscesses in the soft tissues, as well as sinus tracts, and sequestra, although the latter only develop after a period of 30 days or so, and are better demonstrated on CT. A recognised complication of osteomyelitis is the development of an intra-osseous abscess. On T1W
Childhood osteomyelitis presenting as a pathological fracture
images, this will demonstrate a thick, hyperintense, enhancing rim of granulation tissue, around a lowsignal necrotic centre, which is in turn surrounded by low-signal oedema and reactive sclerosis. This has been referred to as the ‘‘penumbra sign’’, and is helpful in differentiating an abscess from a tumour.12 Septic arthritis will demonstrate changes on both sides of the joint, differentiating the reactive joint effusion of osteomyelitis, from a primary or secondary septic arthritis. In infancy, bone marrow in the axial and appendicular skeleton is haemopoeitic (red marrow), and is converted to fatty (yellow) marrow during maturation. Yellow marrow is of high signal on T1W images due to its high fat content, unlike haemopoetic marrow, which will be of low signal on T1W images and patchy on STIR images. In the extremities, conversion occurs first in the epiphysis, followed by the diaphysis, and lastly and incompletely in the metaphysis.13 This may lead to errors in the interpretation of MRI in children, whereby a normal paediatric marrow in the process of conversion, may resemble an osteomyelitic process. A platelet count of >1000 109/l was recorded. Thrombocytosis is not an uncommon phenomenon in paediatric practice, is generally transient, and mainly occurs secondary to infection, chronic inflammation and infantile cortical hyperostosis (Caffey’s disease). Primary causes of a thrombocytosis are very rare, and it has not been documented as occurring in response to fractures.14 The high platelet counts seen in this case would thus indicate an untreated infective or inflammatory process. Finally, it should be noted that a recent course of antibiotics may mask some of the features associated with an osteomyelitis, such as fever and malaise, and result in a more indolent presentation. This has been highlighted in an article describing two children, one of whom had recently been prescribed antibiotics, both of whom looked well and were afebrile, but were found to have an osteomyelitis.15 In summary, this case represents an unusual presentation of osteomyelitis, which is not
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generally listed amongst the causes of pathological fracture.
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