Approach to the Problem
The pattern of a rash can be quite helpful in identifying its etiology. Linear patterns of rashes may be seen in many conditions. In particular, linear red rashes are commonly seen in infectious and inflammatory conditions. They may also be the result of other systemic processes.
Key Points in the History
• A linear red rash that develops after outdoor activity should raise the suspicion of rhus dermatitis due to the exposure to poison ivy, oak, or sumac.
• Rhus dermatitis, scabies, and cutaneous larva migrans are intensely pruritic lesions.
• Children with scabies may have a close contact, who also has an itchy rash. It is helpful to inquire if the parent or another household contact also has a rash, particularly if they share a sleeping surface or bed with the child.
• Lichen striatus may start as a small area of papules that then spreads into a linear distribution.
• Lichen striatus is twice as common in girls than in boys.
• Outdoor exposure to soil or sand that is shared with dogs or cats (e.g., sandboxes) is often a predisposing factor in patients affected with cutaneous larva migrans.
• Linear epidermal nevus, which is not typically pruritic, appears at birth or shortly thereafter.
• Lymphangitis is the secondary manifestation of infection at a distal site. Systemic symptoms of fever, chills, and malaise are often present.
Key Points in the Physical Examination
• Rhus dermatitis is seen on exposed skin, particularly the areas that were exposed while outdoors.
• Excoriation surrounding a linear rash suggests pruritus and scratching, which may lead to bacterial superinfection.
• Red rashes may not be as apparent in individuals with darker skin; therefore, it is important to assess patients in adequate lighting.
• Lichen striatus may appear to be mildly hypopigmented or flesh-colored.
• Infants with scabies often have a generalized rash that includes the soles of their feet. In young children, the rash of scabies is typically seen in the axilla and groin. Older children will often have lesions in the web spaces of their fingers and toes.
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