Morphologically, B. pseudomallei is a gram-negative bacillus with a characteristic bipolar appearance on staining that yields a safety pin appearance.3 It is an exceptionally hardy organism, capable of surviving in extreme environments for extended periods of time.4

Local examination revealed a tender, warm, cystic midline swelling with sero-purulent discharge on his forehead. Neurologic examination did not reveal any focal deficits. Review of cardiovascular, respiratory and gastro-intestinal systems was essentially normal.

Routine laboratory parameters including ESR (10 mm/hr) were unremarkable except for uncontrolled hyperglycaemia with glycosylated haemoglobin (HbA_lc) levels at 9.0%. Cranial MRI confirmed the presence of a scalp collection (Figure 1, Figure 2). The collection was seen to extend through a bony defect in the calvarium into the extradural space with hyperaemia over the adjacent meninges. A left frontal craniotomy was performed under general anaesthesia and the granulation tissue biopsied. Histopathologic examination showed dense fibrocollageneous tissue with infiltration by neutrophils forming microabscesses, surrounded by lymphocytes, histiocytes and areas of caseous necrosis with few palisading epithelioid cells, and dead bony spicules. Although staining for acid-fast bacilli was negative, tuberculosis was suspected based on the characteristic picture of caseating necrosis, the presence of diabetes – a known risk factor for tuberculosis, and the chronic nature of infection. Mantoux test performed was indeterminate with an induration of eight mm. Plain chest X-ray performed was normal, and revealed no stigmata of current or past tubercular infection. Initial culture reports of the pus were sterile. Although the clinical and histopathologic picture was compatible with a tubercular cold abscess, the absence of definitive evidence in the form of absence of acid fast bacilli in the biopsy, absence of radiographic signs of tuberculosis and indeterminate tuberculin skin test, prompted us to await the mycobacterial culture report. The patient was therefore treated with subcutaneous insulin and discharged with instructions to return after one month for follow-up of mycobacterial culture of the biopsy sample. In the event that the culture was positive, we planned to initiate antitubercular drugs in accordance with the DOTS regimen recommended in India. Unfortunately, the patient was subsequently lost for follow-up, returning only after another 11 months. In the interval, the swelling had persisted, now associated with a discharging sinus. Although he had not yet received anti-tubercular therapy in any form, he appeared relatively well. Systemic symptoms were once more conspicuous by their absence. The remarkable indolent nature of the swelling prompted us to review his previous medical records, which revealed that delayed cultures of pus and granulation tissue had grown B. pseudomallei, with a typical sensitivity to co-amoxiclav, ceftazidime, cotrimoxazole and meropenem. A repeat biopsy of the discharging sinus was performed and showed no evidence of tuberculosis. Moreover, mycobacterial culture of granulation tissue from the first biopsy remained sterile.

Having definitively ruled out tuberculosis, pharmacotherapy for melioidosis was initiated with parenteral co-amoxiclav (1.2 g IV q8h) for 14 days, followed by maintenance phase with oral cotrimoxazole (320/1600 mg PO ql2h) for 20 weeks. The patient made a rapid recovery with complete resolution of the discharging sinus and the underlying abscess. After more than a year of follow-up, the patient is healthy with no recurrences.

Our case also represents a rare manifestation of melioidosis. Among the various clinical presentations of B. pseudomallei, pulmonary infection and multiple visceral abscesses are frequently encountered. In contrast, neurological involvement is unusual in melioidosis. A seminal study performed in northern Australia8 identified only 14 cases of neurologic disease in 540 cases over 20 years, while a similar study in Thailand identified only three cases out of 190.9 Vachvanichsanong and colleagues reviewed paediatric cases with neurologic melioidosis and found only eight such cases.10 Furthermore, a proportion of these cases had cerebral abscesses as part of disseminated systemic infection. An Indian study by Kumar et al,11 reported six cases of cranial melioidosis. However, in all these cases, there was either isolated involvement of brain parenchyma in the form of intra-cerebral abscesses or osteomyelitis without extension into the extradural space. Cranial disease produced by local infection or inoculation has been reported in only a handful of studies, including a case series by Chadwick et al12 and a single case report by Kuan et al.13 Interestingly, most of these cases displayed features of severe sepsis. Indeed, the patient reported by Kuan and colleagues13 received prolonged therapy with intravenous meropenem, but succumbed to the disease nonetheless. In contrast, our patient remained relatively asymptomatic despite receiving no treatment for over 11 months. Notably, drainage of the abscess was performed early in our case, when compared to the case described by Kuan. Here surgical drainage of the scalp collection was performed after 12 days of intravenous antibiotic therapy, and intracranial drainage via burr hole was attempted after another fortnight. This suggests that early drainage of such abscesses may play a major role in influencing patient outcomes, perhaps comparable to antibiotic therapy itself. Further study is required to elucidate this possibility.