Differential Diagnosis for the 5-year-old Girl with a Rash
- Single most likely diagnosis
- Scabies: The presence of multiple pruritic lesions in a linear pattern with central hemorrhagic puncta, along with similar lesions in a close contact (the cousin), strongly suggests scabies. The linear pattern is consistent with the burrows caused by the scabies mite.
- Other Likely diagnoses
- Insect bites (e.g., bed bugs, fleas): The arrangement of lesions in a linear pattern could also be seen with insect bites, especially if the insects are feeding in a specific area. The presence of webs in the home might suggest an infestation, but this is more likely to be unrelated to the rash.
- Contact dermatitis: This could be considered if the patient or her cousin came into contact with an allergen or irritant that caused a reaction, leading to the development of erythematous papules. However, the linear pattern and central hemorrhagic puncta are less typical for contact dermatitis.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Tick-borne illnesses (e.g., Lyme disease): Although less likely given the description of the rash and the context, tick-borne illnesses can present with a rash and must be considered, especially if the patient has been in areas where ticks are common. The rash of Lyme disease (erythema migrans) can sometimes appear as multiple smaller lesions, but it typically starts as a single expanding lesion.
- Rare diagnoses
- Delusory parasitosis: This is a psychiatric condition where the patient believes they are infested with parasites, which could lead to scratching and secondary skin lesions. However, the presence of similar lesions in a contact and the specific characteristics of the rash make this less likely.
- Other ectoparasitic infestations (e.g., lice, mites other than scabies): While possible, these are less common and would not typically present with the exact pattern and characteristics described in the scenario.