Vitiligo

A 37-year-old woman comes to her primary care provider for evaluation of skin patches that are lighter in color than the surrounding skin. Her symptoms began 4-months ago and have progressively worsened. The affected areas are non-painful and non-pruritic. Past medical history is notable for type II diabetes mellitus and hypothyroidism, for which she is currently taking metformin and levothyroxine, respectively. Temperature is 37.8°C (100.0°F), blood pressure is 116/73 mmHg, and pulse is 65/min. Physical examination of the patient’s skin reveals the following:

Reproduced from: Wikimedia Commons

Cardiac, pulmonary, and abdominal examinations are noncontributory. Which of the following best describes the pathophysiology of this patient’s condition?