A 45-year-old woman presents with a thickened and yellowed big toe nail. What should be the initial step in managing her condition?

The initial step in managing a patient with a thickened and yellowed big toe nail is to perform a KOH examination of nail scrapings. This procedure is crucial for establishing the correct diagnosis, particularly to determine if the changes in the nail are due to a fungal infection, such as onychomycosis, or another pathology. The KOH examination allows for the identification of fungal elements under a microscope, which is essential for guiding appropriate treatment.

If the underlying cause is indeed a fungal infection, the patient can then be advised on antifungal treatments. Without this initial diagnostic step, other interventions like reassurance, nail removal, or biopsy may not address the root cause of the nail condition and could lead to unnecessary procedures or mismanagement. Therefore, a KOH examination is the most appropriate and effective first step in this scenario, as it provides valuable diagnostic information that influences subsequent management strategies.