Differential Diagnosis for a 10-year-old Girl with Linear Rash
Single Most Likely Diagnosis
- Contact Dermatitis: This is a common condition in children, often caused by exposure to allergens or irritants. The linear pattern of the rash, especially if it appears on areas that could easily come into contact with plants or other allergenic substances (like legs and sometimes arms), supports this diagnosis. The intermittent nature over the last week also fits, as exposure can be sporadic.
Other Likely Diagnoses
- Insect Bites or Stings: These can cause linear or grouped lesions, especially if the child has been outdoors. The pattern and the fact that the rash appears on extremities make this a plausible explanation.
- Phytocontact Dermatitis: This is a specific type of contact dermatitis caused by plants, which can produce linear lesions due to the way the plant comes into contact with the skin. This is common in children who play outdoors.
- Keratosis Pilaris: While not typically linear, keratosis pilaris can sometimes present in a pattern that might be mistaken for a linear rash, especially if the child has dry skin.
Do Not Miss Diagnoses
- Neurocutaneous Syndrome (e.g., Neurofibromatosis): Although rare, conditions like neurofibromatosis type 1 can present with skin manifestations, including café-au-lait spots which might be linear in the case of the "segmental" form. Missing this diagnosis could have significant implications for the child's health and management.
- Infections (e.g., Impetigo, Cellulitis): While less likely given the description, any rash that could be indicative of a bacterial infection needs to be considered, especially if there are signs of infection like redness, warmth, or pus.
Rare Diagnoses
- Lichen Striatus: A rare, self-limiting condition that causes a linear inflammatory rash, typically on one arm or leg. It's more common in children and can appear after a viral infection or as an allergic reaction.
- Linear IgA Bullous Dermatosis: An autoimmune condition characterized by blistering skin lesions that can sometimes appear in a linear pattern. It's rare and would require specific diagnostic tests for confirmation.
- Blaschko Lines: These are congenital conditions that follow the paths of embryonic cell migration and can present with linear rashes or lesions. They are rare and often present at birth or early infancy.