Bacterial Infections

Impetigo - superficial skin infection that is common on kids’ faces. Usually due to Staph aureus > Strep pyogenes. Quite contagious. Presents as red macules that progress to pustules which erupt. Classically has a dry, honey-colored crust. 

Bullous Impetigo - less commonly, Impetigo can create blisters. It only occurs if the Staph possesses an exfoliative toxin to cleave desmosomes (Desmoglein 1) in the stratum granulosum. This is the same toxin seen in SSSS, but this time the toxin is localized.

Staph Scalded Skin Syndrome - a diffuse superficial Staph infection of the skin. The widespread release of exfoliative toxins A and B results in epidermolysis of the stratum granulosum, which causes skin sloughing, redness and fever. It usually affects newborns. It looks terrifying, but the skin will heal back completely. (+) Nikolsky’s sign. No scarring! Treat it with abx. NOTE - the level of skin separation differentiates SSSS from SJS-TEN, where the separation occurs at the dermal-epidermal junction. Also, SSSS spares the palms / soles.

Cellulitis - SO COMMON. It’s an infection of the deep dermis and subQ tissue. It occurs when Staph aureus or Strep pyogenes enter through a break in the skin. They cause the skin to turn red, swollen, tender and warm. The border will be fuzzy. It will gradually grow larger, unless treated with antibiotics.

Erysipelas - infection of the superficial dermis. This is a “textbook term” that doesn’t get discussed much in real life, since it overlaps so much with Cellulitis. It classically occurs on the face and has a very clear border (cellulitis has a fuzzy border). Usually due to Strep. 

Abscess - cellulitis that the immune system has walled off. It’s full of pus, so it feels fluctuant (jiggly) when you poke it. Always caused by Staph aureus. Drain it with a scalpel. Give antibiotics to big ones.  

Necrotizing Fasciitis - infection of the fascia. This is the deepest possible skin infection. Since the fascia is poorly perfused, the immune system can’t stop it! The bacteria chew along the fascia, and fart out CO2 / methane as they go. The gas forms bubbles (crepitus),  which can be detected on the exam (rice crispy texture) or on X-rays (gas bubbles). Furthermore, look for pain out of proportion (POOP) on the physical exam (but in advanced cases the nerves die and it becomes painless). Nec fash can look surprisingly unimpressive early on, but it eventually will look really awful, with blisters and black-and-blue discoloration. Also look for fever and (potentially) hypotension. Surgical Emergency! Needs to be debrided!

Type 1 = the bacteria fart out gas = Clostridium perfringens

Type 2 = no gas = Staph or Strep

Fornier’s Gangrene - necrotizing fasciitis of the groin. It’s nasty. 

Viral Infections

Verruca (Wart) - fleshy papules with a rough surface. Caused by Human Papillomavirus infection of skin cells. Common on the hands and feet (site of viral entry). Histology shows Koilocytosis (halo-shaped cytoplasmic clearing around nuclei). 

Molluscum Contagiosum - firm, pink umbilicated papules caused by the poxvirus. Common in kids, but also seen in promiscuous adults and the immunocompromised. 

Shingles - painful vesicular rash. The shingles rash will be localized to a single unilateral dermatome. The pain precedes the rash by a day or two, making it tough to diagnose at first.