A 52-year-old man with COPD has been using inhaled beclomethasone dipropionate 400 μg daily for 2 years. He now presents with persistent hoarseness, difficulty swallowing, and white plaques in the oropharynx. His physician suspects oral candidiasis secondary to ICS use. Which investigation is most appropriate to confirm the diagnosis?

## Diagnosis of ICS-Induced Oral Candidiasis ### Clinical Context Oral candidiasis is a common local adverse effect of ICS, caused by local immunosuppression and altered oral flora. Confirmation requires direct microbiological evidence. ### Investigation Comparison | Investigation | Diagnostic Value | Sensitivity | When to Use | |---|---|---|---| | **KOH mount & microscopy** | Direct visualization of fungal elements | High (80–95%) | Gold standard for oral candidiasis diagnosis | | Serum IgG antibodies to Candida | Indicates past/chronic exposure, not active infection | Low; non-specific | Not useful for acute oral candidiasis; many healthy people are seropositive | | Chest X-ray | Rules out pulmonary involvement | N/A for oropharyngeal disease | Appropriate only if pulmonary candidiasis is suspected; not diagnostic for oral disease | | OCSS questionnaire | Subjective symptom assessment | N/A; not diagnostic | Useful for severity grading, not diagnosis confirmation | ### Key Point: **KOH (potassium hydroxide) mount and microscopy of an oral swab is the gold standard investigation** for confirming oral candidiasis. It directly visualizes fungal pseudohyphae and spores, providing rapid, cost-effective diagnosis. ### Procedure Details 1. Obtain swab from white plaques or affected mucosa 2. Mix with 10–20% KOH solution 3. Incubate at 37°C for 15–30 minutes 4. Examine under light microscopy for pseudohyphae and budding yeast cells ### Clinical Pearl: Oral candidiasis from ICS is preventable: patients should rinse mouth with water after each ICS dose and use a spacer device to reduce oropharyngeal deposition. If candidiasis develops, topical antifungals (nystatin suspension or miconazole) are first-line; systemic antifungals (fluconazole) are reserved for refractory cases. ### High-Yield: - **KOH microscopy** = rapid, inexpensive, gold standard - **Serum antibodies** = indicate exposure, not active infection; not diagnostic - **Culture** = slower but more specific; reserved if KOH is inconclusive [cite:Park 26e Ch 8; Harrison 21e Ch 212]