What study is most appropriate to confirm the diagnosis of leukoplakia in a patient with a keratinized lesion on the tongue?

To confirm the diagnosis of leukoplakia, an incisional biopsy is the most appropriate study. Leukoplakia manifests as a white patch or plaque on mucosal surfaces, particularly the tongue, and can be a precursor to squamous cell carcinoma. Since leukoplakia may represent dysplastic lesions or malignancy, histopathological examination through a biopsy is crucial. An incisional biopsy allows for sufficient tissue sampling to evaluate the presence of dysplasia or malignancy, providing definitive diagnostic information.

Other methods, although helpful in diagnosing different conditions, do not provide the same level of diagnostic clarity for leukoplakia. A Tzanck smear is used primarily to identify herpes infections by revealing multinucleated giant cells but does not contribute to diagnosing leukoplakia. A Gram stain is useful for identifying bacterial infections but is unrelated to the assessment of keratinized lesions. Lastly, a potassium hydroxide (KOH) wet prep is typically used to diagnose fungal infections by clearing keratin, allowing fungal elements to be visualized; this method does not apply to leukoplakia. Therefore, an incisional biopsy stands out as the definitive method to diagnose and assess the potential risk of malignancy in leukoplakia.