A 40-year-old man is found to have severe metabolic acidosis with a high anion gap. What is the most likely cause?

Methanol ingestion results in increased production of lactic acid causing an increased anion gap. The other conditions listed are associated with normal anion gap. Diarrhea, proximal renal tubular acidosis, and ureterosigmoidostomy result in loss of bicarbonate, while distal renal tubular acidosis is associated with decreased acid excretion.