What physical exam finding is pathognomonic for appendicitis?

McBurney's point tenderness is recognized as the pathognomonic physical exam finding for appendicitis. This localized tenderness occurs in the right lower quadrant of the abdomen, specifically at the point that is two-thirds of the distance from the umbilicus to the anterior superior iliac spine (ASIS). The significance of this finding lies in its strong correlation with the location of the appendix, which, when inflamed, typically presents with tenderness in this precise area.

This tenderness is a direct result of inflammation of the vermiform appendix, which irritates the surrounding peritoneum and causes pain upon palpation. While other signs, such as the obturator sign and psoas sign, indicate the presence of peritoneal irritation due to possible appendicitis or adjacent pathology, they are not exclusively associated with appendicitis itself. Rectal tenderness can suggest a range of abdominal conditions and is therefore not specific to appendicitis.

In summary, McBurney's point tenderness is a classic and defining physical exam finding for appendicitis, reflecting the anatomical relationship of the inflamed appendix to the abdominal wall and facilitating diagnosis during a clinical examination.