Tunnel sign on magnetic resonance imaging in neuromelioidosis: A systematic literature review

Background: Neuromelioidosis can present with abscesses, meningitis, or encephalomyelitis, but can be missed on blood culture. Linear enhancement of the corticospinal tract (white matter motor pathway) on magnetic resonance imaging (MRI) in the form of a ‘tunnel sign’ is an essential clue for early diagnosis of neuromelioidosis. This systematic review (SR) explores the clinical profile and outcomes of neuromelioidosis patients with tunnel signs. Methods: An SR was conducted to look for articles reporting individual details of neuromelioidosis patients with tunnel signs (reported or present on published images) on MRI. This review followed PRISMA guidelines and was prospectively registered with PROSPERO (CRD42024597199). After title-abstract and full-text screening, clinical profile and outcome data were extracted and analysed. Results: Thirty cases (22 articles) with tunnel signs on MRI were included after screening 2985 articles. The traditional risk factors (diabetes mellitus, alcohol intake, steroids, etc.) for melioidosis were present in only 23 % (5/22) of patients. Limb weakness (89 %, 24/27) and cranial nerve involvement (46 %, 11/24) were commonly seen at presentation. Blood and cerebrospinal fluid (CSF) cultures for B.pseudomallei were only positive in 15 % (2/13) and 22 % (4/18). Due to low rates of clinical suspicion of neuromelioidosis (25 %, 6/24), empirical steroids and inappropriate antimicrobials were given in 47 % (8/17) and 65 % (9/17) of patients, respectively. A total of 30 % (n = 9) of the patients died. Conclusion: In melioidosis-endemic areas with access to MRI, recognising the link between the presence of a tunnel sign and neuromelioidosis is crucial to initiate early adequate therapy.