A 35-year-old man with newly diagnosed pulmonary tuberculosis is started on standard 4-drug therapy including isoniazid. He is a slow acetylator of isoniazid (genetic polymorphism in N-acetyltransferase). The structure marked **A** in the diagram is the target of isoniazid action. Which of the following adverse effects is this patient at HIGHEST risk of developing due to his slow acetylator phenotype?