John Gill Commentary 2 Chronicles 21:18

"And after all this Jehovah smote him in his bowels with an incurable disease." — 2 Chronicles 21:18 (ASV)

After all this the Lord smote him in his bowels with an incurable disease. What it was is not agreed upon; some take it be an "hernia", or rupture; others, the falling of the "anus", or a fistula in it; others, the colic, or iliac passion; but generally it is thought to be a dysentery, or bloody flux; the Targum is, "the Word of the Lord broke him."