RARE CASE OF POTT'S DISEASE CAUSED BY BACILLUS‐CALMETTE GUÉRIN VACCINE

A previously well 13-month-old girl presented with gradual loss of ability to stand and crawl over a 2-month period. Physical examination revealed spastic paraparesis, bilateral extensor plantar responses and hyperreflexia of her legs. Magnetic resonance imaging of the spine demonstrated an extradural tissue mass from C5 to T4 causing cord compression and simultaneous disease involvement of T1/2 vertebral bodies. Overall, the features were suspicious for neuroblastoma (Fig. 1a,b). She underwent laminoplasty and biopsy of the extradural mass. Histopathology reported granulomatous inflammation (Fig. 1c). She was commenced on anti-tuberculous treatment consisting of rifampicin, isoniazid, ethambutol and pyrazinamide. Pyrazinamide was stopped when Mycobacterium bovis Bacillus-Calmette Guérin (BCG) was confirmed on Acid-Fast Bacillus (AFB) culture of the mass, with the remaining treatment continued for a 9-month course. She had received the BCG vaccine (Tokyo strain) at birth and did not consume any unpasteurised cow's milk. Investigations for immunodeficiency, including immunoglobulin levels, lymphocyte subsets, testing for Mendelian susceptibility to mycobacterial disease and next generation sequencing tests for primary immunodeficiencies, all returned negative. She has since caught up on her developmental milestones, with resolution of spastic paraparesis, and at 21 months old is able to walk independently. We present a rare case of Pott's disease caused by BCG vaccine. Although magnetic resonance imaging is the imaging modality of choice for Pott's disease, with high sensitivity and specificity,1 our case suggests that its presentation can mimic spinal tumours. BCG vaccine is a live attenuated strain of M. bovis, and is routinely administered at birth to all newborns in Singapore since the mid-1950s to prevent tuberculosis.2 Although generally well tolerated, local complications, such as ulcers, abscesses or regional suppurative lymphadenitis may occur.3 In view of the current considerations that immune-boosting properties from BCG vaccine can act as a protective measure against COVID-19 infection,4 it is important to note that rare, severe and potentially fatal complications such as disseminated BCG infection may occur, even in otherwise immunocompetent individuals. Correct diagnosis and initiation of appropriate therapy in BCG Pott's disease is important to reduce the risk of permanent deformities and paraplegia. Patients should also be concurrently investigated for an underlying immunodeficiency.