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When a radionuclide bone scan shows multiple areas of high uptake, infective as well as metastatic disease must be considered.
A Pakistani man aged 48 sought advice about right-sided rib pain. The pain could be reproduced by pressure over the right 2nd and 4th ribs but clinical examination was otherwise unremarkable. Musculoskeletal chest pain was diagnosed and he was advised to use non-steroidal analgesia. Three months later he returned with similar rib pain. The only abnormality on blood testing was a raised C-reactive protein, and the chest radiograph showed nothing of note. To exclude pulmonary embolism a CT pulmonary angiogram was performed. No emboli were seen but the images revealed a soft tissue mass affecting the right second rib. A radionuclide bone scan then disclosed multiple uptake sites along the axial skeleton highly suggestive of metastatic malignant deposits (Figure 1a). However, CT examination of the chest and abdomen, tumour markers and protein and urine electrophoresis offered no clues to their origin. The next investigation was fine needle aspiration of the rib lesion, which revealed granulomatous inflammatory change consistent with sarcoidosis or tuberculosis (TB). Microscopy was negative for acid-fast bacilli, as were polymerase-chain-reaction-based tests for Mycobacterium tuberculosis complex DNA. The level of serum angiotensin converting enzyme was also normal. The patient did not report night sweats, weight loss, or a past or family history of tuberculosis. He had received BCG vaccine at age 6 years. Three early-morning urine samples sent for M. tuberculosis culture were sterile. A Heaf test produced only a grade 1 result. A further rib lesion was examined, with results similar to those of the previous biopsy. Subsequently, cultures of both fine needle aspirates were reported positive for M. tuberculosis, sensitive to rifampicin, pyrazinamide and ethambutol but resistant to isoniazid. The patient was started on antituberculosis therapy. Ten months later a bone scan showed a reduction in the number and intensity of areas of radionuclide uptake (Figure 1b).
In the UK, TB is more likely to be extrapulmonary in persons from the Indian subcontinent than in the indigenous white population. In a 1993 study, 241 out of 1075 notified cases in the white population were extrapulmonary (22%) compared with 428 of 1040 in patients from the subcontinent (41%).1 The contributions of bone disease to extrapulmonary TB in these populations were very similar (15% and 14%). Multifocal osteoarticular TB can be defined as two or more non-contiguous simultaneously occurring lesions involving bones and/or joints.2,3 Around 10% of patients with skeletal tuberculosis have been shown to have multifocal lesions2—possibly an underestimate, since radiographic changes may be delayed, and areas of disease may be clinically silent.4
In the present case radionuclide scans raised the possibility of metastatic malignant disease, though TB was considered from an early stage. The distribution of the lesions was atypical for TB (the ribs are involved in only 1-5% of patients with osteoarticular tuberculosis2) but the diagnosis was not ruled out by the lack of a strong Heaf reaction and absence of visible acid-fast bacilli in the biopsy specimens. We are not the first to encounter a disturbing bone scan in these circumstances.5 Areas of high uptake merely reflect increased bone turnover6 and, as with all radiological investigations, bone scans must be interpreted in the context of the clinical presentation.