Bacterial and viral skin infections: Pathology review

At the clinic, 10-year-old Quentin is brought by his parents after an episode of dark-colored urine. Upon examination, his blood pressure is high and you notice that the area around his ankles appears swollen. His parents also mention that last week, Quentin developed multiple vesicles with a honey-colored crusting around his nose and mouth. You decide to perform a urinalysis test, which reveals there’s blood in the urine with red blood cell casts, as well as higher than normal levels of protein.

Later on that same day, 70-year-old Claudio presents to the emergency department complaining of severe pain in his genital area that started about a week ago. On examination, you notice severe scrotal swelling, a purplish rash, and palpable crepitus in the perineal area. Claudio also appears lethargic, and has a fever and low blood pressure. Upon further questioning, Claudio mentions that he had surgery for varicocele about two weeks ago. Past medical history reveals that in his 40s, Claudio was diagnosed with diabetes mellitus, which he has not been controlling properly. You decide to order a swab culture, which comes back positive for anaerobic bacteria and Streptococcus pyogenes.

Based on the initial presentation, both Quentin and Claudio seem to have some form of skin infection.

Okay, first, let’s go over some physiology. Normally, the skin is divided into three main layers, the hypodermis, dermis, and epidermis. The hypodermis is made of fat and connective tissue that anchors the skin to the underlying muscle. Above the hypodermis is the dermis, which contains hair follicles, nerve endings, glands, blood vessels, and lymphatics. And above the dermis is the epidermis, which contains five layers of developing keratinocytes.

Keratinocytes start their life at the lowest layer of the epidermis, so the stratum basale or basal layer. As keratinocytes in the stratum basale mature, they migrate up into the next layers of the epidermis, called the stratum spinosum, stratum granulosum, stratum lucidum, and finally, the stratum corneum, which is the uppermost and thickest epidermal layer.