Diagnostic utility of Chicago sky blue stain in superficial dermatophytosis
Keywords:CSB, Culture, Dermatophytosis, Potassium hydroxide mount
Background: Dermatophyte infections are one of the commonest presentations to a dermatology OPD. The clinical lesions are highly variable and closely resemble other skin diseases, thus it is important to confirm one’s diagnosis using rapid, cheap methods.
Methods: Skin scrapings from the lesions of 352 suspected cases of dermatophytosis were subjected to KOH mount and KOH with Chicago sky blue (CSB) stain for direct microscopic examination and culture using Sabouraud’s dextrose agar (SDA). Taking the culture as the gold standard method for diagnosis, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) of KOH mount and CSB staining method was calculated. Kappa statistics were used to determine the degree of congruence between the various diagnostic methods.
Results: Direct microscopy with CSB stain, KOH mount and mycological culture showed positive results in 251 (71.3%), 227 (64.5%) and 292 (82.9%) patients, respectively. Cohen’s Kappa was used to see the agreement between KOH mount and culture (Kappa=0.09) which was statistically significant (p<0.05) at 95% CI. CSB staining and Culture (Kappa=0.09) also showed negligible agreement (Kappa=0.09) which was statistically significant (p<0.05). CSB staining and KOH mount showed substantial agreement (Kappa=0.8) which statistically significant (p<0.05).
Conclusions: The addition of CSB stain to KOH provides a colour contrast that highlights the fungal elements well, making interpretation easy which increases the overall diagnostic accuracy. CSB stain is inexpensive, easily available and provides a rapid method to diagnose dermatophytosis.
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