A 55-year-old woman with uncontrolled diabetes develops facial pain, proptosis, and a black eschar on the right nasal turbinate. KOH mount of debrided tissue shows broad, ribbon-like, aseptate hyphae with right-angle branching. Serum beta-D-glucan is negative and serum galactomannan index is 0.1. How should these biomarker results be interpreted?
- A Negative BDG and GM are expected in mucormycosis, and the diagnosis rests on microscopy and histopathology ✓
- B They effectively exclude invasive fungal disease
- C They confirm colonisation rather than invasion
- D They indicate infection by an uncommon yeast such as Cryptococcus
Correct answer: A. Negative BDG and GM are expected in mucormycosis, and the diagnosis rests on microscopy and histopathology
Explanation
Mucorales are detected poorly or not at all by both beta-D-glucan and galactomannan assays, so negative results never exclude mucormycosis. Diagnosis depends on direct microscopy and histopathology showing broad aseptate hyphae invading tissue and vessels. The clinical picture here is classic rhino-orbital mucormycesis in diabetic ketoacidosis. Cryptococcus produces a strongly positive cryptococcal antigen and budding encapsulated yeast, not ribbon-like hyphae.
Reference: Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.