Differential Diagnosis for Rash and Right Lower Abdomen Pain

Single Most Likely Diagnosis

• Viral Gastroenteritis: This condition often presents with abdominal pain, which can be localized to the right lower quadrant, and can be accompanied by a rash in some cases, especially if the causative virus has a dermatological manifestation.

Other Likely Diagnoses

• Urinary Tract Infection (UTI): A UTI, particularly pyelonephritis, can cause abdominal pain that might be perceived in the right lower quadrant and could be accompanied by a rash if there's an allergic reaction to antibiotics or if the infection leads to a systemic response.
• Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause abdominal pain and may be associated with extraintestinal manifestations, including skin rashes.
• Henoch-Schönlein Purpura (HSP): This is a form of vasculitis that affects blood vessels and is characterized by a rash (purpura), abdominal pain, and sometimes joint pain or kidney involvement.

Do Not Miss Diagnoses

• Appendicitis: Although appendicitis typically presents with right lower quadrant pain without a rash, in rare cases, a rash could be present due to a secondary infection or an allergic reaction. Missing appendicitis can lead to severe consequences, including perforation and peritonitis.
• Ectopic Pregnancy: In women of childbearing age, ectopic pregnancy is a critical diagnosis to consider with abdominal pain, even if a rash is present. The rash could be unrelated or a sign of a concurrent condition.
• Diverticulitis: While less common in the right lower quadrant, diverticulitis can cause severe abdominal pain and might be accompanied by a rash if there's an associated infection or allergic reaction.

Rare Diagnoses

• Ehlers-Danlos Syndrome: This is a group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. Some types can cause abdominal pain and skin manifestations, including rashes.
• Sarcoidosis: A condition that can cause inflammation in various parts of the body, including the skin (leading to rashes) and the abdomen (causing pain).
• Kawasaki Disease: An acute febrile illness of childhood characterized by inflammation in the walls of medium-sized arteries throughout the body, which can cause rash, abdominal pain, and other systemic symptoms.