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Purple pleural fluid secondary to Acinetobacter baumannii infection
  1. Ketan Agarwal,
  2. Ratnadeep Biswas and
  3. Ravi Kirti
  1. Department of General Medicine, All India Institute of Medical Sciences - Patna, Patna, Bihar, India
  1. Correspondence to Dr Ratnadeep Biswas; ratnadeepbis2404{at}

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A male patient in his 30s, who was a known case of chronic kidney disease (on maintenance haemodialysis) secondary to diabetes mellitus, was presented with worsening of breathlessness for 2 days. He came with an intercostal drain (ICD) in situ, already inserted at another hospital, in view of a massive effusion causing severe shortness of breath. He had been taking antitubercular drugs for the previous 13 days. Chest auscultation revealed decreased air entry on the right side and bilateral crepitations. High-resolution CT of the thorax showed bilateral pleural effusion (right > left) with thickened pleura and loculations on the right side and hyperdense contents suggestive of haemorrhage (figure 1). Minimal pericardial effusion and bilaterally enlarged paratracheal and paraaortic nodes were also seen. Haemodialysis was done, and the ICD was changed. Two days later, a purple discolouration of the ICD was noted (figure 2). Analysis of the pleural fluid revealed 7–10 pus cells per low power field and Gram-negative cocco-bacilli. Culture of the fluid grew Acinetobacter baumannii sensitive only to colistin. Biochemical analysis revealed high levels of adenosine deaminase (73 U/L), low glucose levels (27 mg/dL), a low pH (7.1) and high protein levels (3 g/dL). The blood culture report was sterile. The patient was continued on antitubercular therapy, and intravenous colistin (loading dose of 300 mg of colistin base activity (CBA), followed by a maintenance dose of 180 mg CBA on haemodialysis days and 130 mg CBA on non-dialysis days) and intravenous meropenem (loading dose of 1 g given over 30 min, followed by 500 mg given over 3 hours by the extended infusion method on haemodialysis days) were added. Unfortunately, the patient’s clinical condition continued to deteriorate, and he suffered a cardiac arrest on day 26, from which he could not be revived.

Figure 1

CT of the thorax shows dense, fluid-filled pleural layers with collapsed lung lobes, confluent ground-glass opacities in the left upper lobe indicating atypical pneumonia and air within pleural fluid due to an inserted chest tube.

Figure 2

Intercostal drain of the patient shows pleural fluid with purple discolouration (A), and the ICD of another patient in (B) exhibits dark haemorrhagic fluid for comparison.

Purple discolouration of the pleural fluid is a rare phenomenon that occurs most likely due to the breakdown of tryptophan metabolites into indoxyl by bacterial phosphatases and sulfatases, which break down into indigo (blue) and indirubin (red), a pathophysiology analogous to the purple urine bag syndrome.1 Such discolouration of pleural fluid should prompt the physician to consider the possibility of bacterial infection and initiate treatment accordingly while awaiting confirmation.

Learning points

  • Purple pleural fluid is an extremely rare finding and likely occurs due to a bacterial infection producing certain coloured compounds.

  • Bacterial phosphatases and sulfatases breakdown tryptophan metabolites to ultimately produce indigo (blue) and indirubin (red), which provide the purplish hue.

  • Such discolouration of the pleural fluid should alert the physician to the possibility of bacterial infection and initiate treatment.

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  • Contributors All authors were responsible for the drafting of the text, sourcing and editing of clinical images, investigation results, drawing original diagrams and algorithms, critical revision for important intellectual content, patient care and final approval of the manuscript. KA got the image. RB wrote the initial draft of the manuscript. RK and KA edited the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.