Differential Diagnosis for Linear Rash Down Shin Region and Diarrhea

• Single Most Likely Diagnosis
  • Dermatitis Herpetiformis: This condition is characterized by a linear, itchy rash often found on the elbows, knees, and buttocks, but can also appear on the shin region. It is associated with celiac disease, which can cause gastrointestinal symptoms like diarrhea. The rash and diarrhea connection makes this a strong candidate.
• Other Likely Diagnoses
  • Contact Dermatitis: This is a type of inflammation of the skin that occurs when the skin comes into contact with an irritant or allergen, leading to a rash. If the irritant or allergen comes into contact with the shin, it could cause a linear rash. Diarrhea could be unrelated or due to a separate cause.
  • Insect Bite or Sting Reaction: Linear patterns can occur if the individual has been walking through an area with insects that bite or sting in a line (like certain types of caterpillars). Diarrhea might not be directly related but could be a coincidental symptom.
  • Phytophotodermatitis: This condition occurs when the skin reacts to certain plant chemicals (like those in lime juice or certain weeds) after exposure to sunlight, leading to a rash. The pattern can be linear if the exposure was in a line. Diarrhea is unlikely to be directly related.
• Do Not Miss Diagnoses
  • Neurogenic or Neurocutaneous Disorder: Certain conditions like neurofibromatosis can present with skin manifestations and gastrointestinal symptoms. Although less common, missing these diagnoses could have significant implications.
  • Vasculitis: Conditions that cause inflammation of the blood vessels can lead to skin rashes and systemic symptoms, including gastrointestinal issues like diarrhea. Missing vasculitis could lead to serious complications.
• Rare Diagnoses
  • Erythema Marginatum: A rash associated with acute rheumatic fever, which could theoretically present with a linear pattern, though this is less common. Diarrhea is not typically a primary symptom but could occur due to other related conditions.
  • Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis): Characterized by fever, neutrophilia, and tender, erythematous skin lesions. While the rash is typically not linear, and diarrhea is not a hallmark symptom, Sweet Syndrome can present with a wide range of skin manifestations and systemic symptoms.