Hansen Leprosy Multibacillary Nodules

A 42-year-old construction worker from an endemic district presents with a 3-year history of progressive painless skin lesions, nasal stuffiness, and sensory loss in the extremities. On examination, he has the characteristic appearance shown in the diagram with symmetric infiltrated plaques on the cheeks and forehead (marked **B**), along with madarosis, earlobes nodularity, and copper-coloured nodules on the extensor forearms. Slit-skin smears show numerous acid-fast bacilli with a bacterial index of 5+. Last week he developed painful erythematous nodules on the shins with fever. Which of the following best explains the acute systemic manifestation that prompted this presentation?