Utility of Three-phase Skeletal Scintigraphy with Single Photon Emission Computed Tomography/Computed Tomography in a Case of Chronic Recurrent Multifocal Osteomyelitis

Sir,

Chronic recurrent multifocal osteomyelitis (CRMO) is a rare disease with unknown etiology. It is often considered as an auto-inflammatory disorder and may mimic as bacterial osteomyelitis.[1] CRMO is often reported in the childhood and adolescence. It is characterized by recurrent episodes of unprovoked inflammation of skeletal sites with resultant destruction and painful swelling during its active phase and (often) a painless benign asymptomatic reparative phase. The diagnosis of CRMO is often by exclusion and is usually characterized by (i) absence of features of typical osteomyelitis (such as presence of sequestrum, abscess, or fistula formation); (ii) protracted course with frequent remissions and exacerbations; (iii) atypical and multifocal nature of skeletal involvement; (iv) no pathogenic organisms on tissue culture; (v) nonspecific findings of subacute/chronic osteomyelitis on histological evaluation; (vi) poor response to antimicrobial therapy; and (vii) association with palmoplantar pustulosis, acne, or other inflammatory disorders.[2] The imaging and histological studies can assist in the exclusion of possible alternate diagnoses and establishing the diagnosis of CRMO.

We here present a case of 18-year-old male adolescent presented with progressive swelling over the left lower neck region associated with pain and pruritus for 3 months. Oral nonsteroidal anti-inflammatory drugs relieved the pain briefly with frequent relapse. X-ray and magnetic resonance imaging (MRI) of the upper thoracic region revealed expansile destructive lesion involving the medial third of left clavicle and sternum with periosteal reaction and associated soft tissue changes, suggesting an infective/neoplastic lesion. Biopsy of the lesion for further characterization demonstrated the findings consistent of chronic osteomyelitis, without significant growth of any pathogenic organisms on culture of the biopsied material.

A three-phase skeletal scintigraphy (TPSS) after intravenous injection of 20 mCi of ^99mTc-methylene diphosphonate was performed to assess the activity status of the clavicular lesion and screen the additional skeletal involvement. Mildly increased perfusion, tracer pooling, and tracer avidity were noted in the medial half of the left clavicle and adjacent body of the sternum in all three phases of regional skeletal scintigraphy [Figure 1a–e]. Whole-body images [Figure 2a and b] showed additional focally increased tracer uptake in the left sacroiliac joint, with clinical correlation of recent onset of pain in the same region. The tracer avid mixed lytic-sclerotic expansile lesion of medial two-third of the left clavicle and a sclerotic lesion in sternum near manubriosternal joint were seen on hybrid single photon emission computed tomography/computed tomography (SPECT/CT) of the neck and upper chest region [Figure 2c–h].

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Figure 1 Tc-99m-methylene diphosphonate three-phase skeletal scintigraphy, anterior flow images (a) and anterior and posterior blood pool images of the neck and thoracic regions (b and c) showing increased blood flow and soft tissue blood pooling in the left clavicular region. Delayed anterior and posterior bone static images (d and e) showing increased osteoblastic activity in the medial two-third of the left clavicle and upper body of the sternum. Uptake in the sternum is not conspicuous on flow and blood pool images due to physiological mediastinal blood pool activity

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Figure 2 Tc-99m-methylene diphosphonate skeletal scintigraphy (a and b) anterior and posterior whole-body images showing increased osteoblastic activity in medial two-third of the left clavicle, body of the sternum, and left sacroiliac joint; coronal CT (c and d), SPECT (e and f), and SPECT/CT (g and h) of the thorax showing increased osteoblastic activity in mixed lytic-sclerotic expansile lesion and in the medial two-third of the left clavicle and sclerotic lesion in the upper body of the sternum near manubriosternal joint. SPECT/CT: Single photon emission computed tomography/computed tomography

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Auto-inflammatory skeletal disorders such as CRMO often result from the dysregulation of innate immunity, leading to immune cell infiltration of the bone and consequent osteoclastic activation, osteolysis, and reparative bone remodeling, though exact molecular event inciting this is not fully understood.[3] Strong association of CRMO with various other inflammatory disorders such as palmoplantar pustulosis, acne, psoriasis, sweet syndrome, and inflammatory bowel disease is well established. Synovitis, acne, pustulosis, hyperostosis, and osteitis syndrome is a similar auto-inflammatory disorder and often considered as the adult counterpart of CRMO. Patients with CRMO usually present with insidious onset of pain and swelling of the involved bones.[4] The commonly involved sites include the medial ends of the clavicles and metaphyses of long tubular bones of lower limbs, followed by flat bones such as pelvis and sternum.[5] Typically, the course of the disease is prolonged with alternating exacerbations and remissions. Recurrence may involve previously involved sites or new sites. Flare-ups of the associated auto-inflammatory disorders are noted simultaneous to the osseous exacerbations, suggesting common etiological basis.[2]

Conventional radiography is the first-line investigation in providing the site and nature of the involvement followed by CT and MRI, facilitating the better characterization of the lesions. TPSS is a widely established nuclear medicine imaging modality for the evaluation of suspected osteomyelitis with high sensitivity in unviolated bones. Active osteomyelitis is often characterized by the presence of increased flow; blood pooling and tracer uptake on TPSS.[6] Whole-body imaging detects clinically silent distant diseased sites. Mandell et al. demonstrated the utility of whole-body bone scan in 14 patients with CRMO in detecting the multifocality and in selection of biopsy sites.[7] SPECT/CT allows for precise anatomical localization, extent of the disease, and characterization of the lesions. In the present case, TPSS with SPECT/CT revealed bony lesions at primary site and additional site of involvement in the left sacroiliac joint correlating with the recent onset of pain at the same site. TPSS with SPECT/CT has potential role in accurate assessment of disease activity, detection of additional occult sites of involvement with better characterization of the lesions, and anatomical identification of optimal sites for biopsy evaluation, thus furnishing as a one-stop-shop imaging technique.