Differential Diagnosis
- Single most likely diagnosis
- Impetigo: This is a highly contagious bacterial skin infection that can spread quickly among family members, especially in close living conditions. The presence of a blister on the sister's hand, which could be a sign of a spreading infection, supports this diagnosis.
- Other Likely diagnoses
- Herpes Simplex Virus (HSV): HSV can cause blisters and is contagious, spreading through skin-to-skin contact. The appearance of a blister on the sister's hand could be indicative of HSV infection.
- Varicella (Chickenpox): Although less common in an era of widespread vaccination, chickenpox can cause blisters and is highly contagious, spreading through the air when an infected person coughs or sneezes or by touching a rash.
- Contact Dermatitis: This condition can cause blisters and can spread through contact with an allergen or irritant that has come into contact with the skin.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Meningococcemia: Although rare, this condition can present with skin lesions (including blisters) and is life-threatening if not promptly treated. It's essential to consider this diagnosis, especially if there are signs of systemic illness.
- Staphylococcal Scalded Skin Syndrome (SSSS): Caused by staphylococcal toxins, SSSS can lead to widespread skin lesions and is more common in children. It requires immediate medical attention.
- Rare diagnoses
- Hand, Foot, and Mouth Disease (HFMD): Typically affecting younger children, HFMD can cause blisters on the hands and feet, as well as in the mouth. It's contagious and usually self-limiting but can be considered in the differential.
- Pemphigus: An autoimmune disease that causes blistering of the skin and mucous membranes. It's rare and would be unusual in siblings unless there's a genetic predisposition.
- Epidermolysis Bullosa: A group of genetic conditions that result in fragile skin and blisters. While rare, it could be considered if there's a family history or if the blisters are not responding to typical treatments for infectious causes.