A 68-year-old woman from Mumbai presents with sudden onset of velvety, hyperpigmented plaques over the neck, axillae, and inframammary folds over 3 months. She has no significant past medical history, BMI 22 kg/m², normal fasting glucose, and no family history of diabetes. Physical examination reveals extensive acanthosis nigricans with keratotic papules. What is the most appropriate next step in management?