Candidiasis — SAQ

Stem

A 32-year-old woman with type 2 diabetes mellitus and obesity presents with a 10-day history of an itchy, painful rash in both inframammary folds and the groin. The rash is bright red, moist and has a few surrounding small pustules. She recently completed a course of amoxicillin-clavulanate for a chest infection. She also notices a white coating on her tongue that can be scraped off, leaving a red base. On examination, there are erythematous plaques in the skin folds with well-defined margins and satellite papules and pustules. A skin scraping shows budding yeasts and pseudohyphae on 10% potassium hydroxide (KOH) microscopy.

Questions

a) What is the most likely diagnosis, and what are the characteristic clinical features? (2 marks)

b) List the predisposing factors in this patient and explain how each contributes to candidal infection. (2 marks)

c) What is the bedside investigation of choice, and how does it differentiate Candida from dermatophyte infection? (2 marks)

^[6]d) Outline the stepwise management of this patient, including both local and systemic measures. (2 marks)

e) What additional investigations would you consider if the oral candidiasis was severe, recurrent or if she had no obvious risk factors? (2 marks)

Model answer

a) Diagnosis and clinical features

The most likely diagnosis is cutaneous candidiasis (candidal intertrigo) with oropharyngeal candidiasis (thrush). The characteristic features of intertrigo are an intensely erythematous, moist, macerated plaque in a skin fold with a collarette of scale and satellite papules or pustules at the periphery. Oral thrush presents as white, curd-like plaques that can be scraped off to reveal an erythematous or bleeding base. The diagnosis is supported by the presence of budding yeast and pseudohyphae on KOH.^[4]

^[4]b) Predisposing factors

1. Diabetes mellitus: hyperglycaemia impairs neutrophil chemotaxis and phagocytosis, and glycosuria provides a glucose-rich environment for yeast growth.
2. Obesity: increased skin-fold surface area, moisture, friction and occlusion create an ideal environment for Candida overgrowth.
3. Recent broad-spectrum antibiotics: reduce competing bacterial flora, allowing Candida to proliferate on skin and mucosa.
4. Skin folds (intertrigo): warmth, moisture and maceration disrupt the epithelial barrier and promote yeast invasion.

c) Bedside investigation and differential microscopy

The bedside investigation is 10% potassium hydroxide (KOH) microscopy of skin scrapings or mucosal smears. In candidiasis, microscopy shows ovoid budding yeasts and pseudohyphae (elongated chains of yeast cells that remain attached). Dermatophytes, by contrast, show branching, septate hyphae without budding yeast forms. The presence of pseudohyphae supports Candida; culture is reserved for recurrent, refractory or severe disease, or when species identification is needed.^[4]

^[1][3]d) Stepwise management

• General measures: keep folds dry, use loose cotton clothing, reduce friction, and address weight loss if obese. Dry skin folds thoroughly after bathing.
• Oral therapy: if intertrigo is extensive, recurrent or fails topical therapy, use oral fluconazole (150 mg weekly, or 100–200 mg daily for 7–14 days for severe oral thrush).^[6]
• Risk-factor control: optimise glycaemic control and avoid unnecessary antibiotics.
• Secondary bacterial infection: if purulent satellite lesions or cellulitis are present, add a topical or oral antistaphylococcal agent.

^[2]e) Additional investigations

If oral candidiasis is severe, recurrent, or occurs without obvious risk factors, investigate for an underlying predisposing condition:^[6]

• Fasting glucose or HbA1c for diabetes (already known here, but assess control).
• HIV Ag/Ab testing because oral and oesophageal candidiasis are classic AIDS-defining opportunistic infections, especially when CD4 count is less than 200 cells per microlitre.
• Iron studies, ferritin, folate and vitamin B12 if angular cheilitis or persistent oral candidiasis is present.
• Endoscopy if there are symptoms of oesophageal involvement such as dysphagia or odynophagia, particularly in HIV-positive patients.
• Immunology/genetic referral if chronic mucocutaneous candidiasis is suspected from infancy, with screening for STAT1 gain-of-function, AIRE/APECED and IL-17 pathway defects.