USMLE Guide: Skin Infections

Introduction

Skin infections are a common health concern that affects individuals of all age groups. It is important for healthcare professionals to have a comprehensive understanding of different types of skin infections, their underlying causes, clinical presentation, diagnostic approaches, and treatment options. This USMLE guide aims to provide a concise overview of skin infections to help medical students and professionals prepare for the USMLE exam.

Table of Contents

1. Bacterial Skin Infections
2. Viral Skin Infections
3. Fungal Skin Infections
4. Parasitic Skin Infections
5. Common Clinical Presentations
6. Diagnostic Approaches
7. Treatment Options

Bacterial Skin Infections

• Impetigo: Superficial infection caused by staphylococcus aureus or Streptococcus pyogenes. Presents as honey-colored crusts or vesicles. Treatment involves topical antibiotics (e.g., mupirocin) or systemic antibiotics (e.g., dicloxacillin).
• Cellulitis: Infection of the dermis and subcutaneous tissues commonly caused by streptococcus pyogenes or Staphylococcus aureus. Presents with erythema, warmth, and swelling. Treatment involves systemic antibiotics (e.g., cephalexin).
• Erysipelas: Superficial form of cellulitis caused by beta-hemolytic streptococci. Presents with sharply demarcated erythematous plaques and fever. Treatment involves systemic antibiotics (e.g., penicillin).

Viral Skin Infections

• herpes simplex Virus (HSV): Causes painful grouped vesicles on an erythematous base. HSV-1 causes oral lesions, while HSV-2 causes genital lesions. Treatment involves antiviral medications (e.g., acyclovir).
• Varicella-Zoster Virus (VZV): Causes chickenpox (varicella) and shingles (herpes zoster). Presents with vesicular rash and dermatomal distribution in herpes zoster. Treatment involves antiviral medications (e.g., acyclovir).
• Molluscum Contagiosum: Viral infection caused by the poxvirus. Presents with flesh-colored, dome-shaped papules with central umbilication. Spontaneous resolution is common, but treatment may include cryotherapy or curettage.

Fungal Skin Infections

• tinea corporis (Ringworm): Caused by dermatophyte fungi. Presents with annular, scaly, pruritic plaques. Treatment involves topical antifungal agents (e.g., terbinafine).
• Tinea Pedis (Athlete's Foot): Fungal infection of the feet. Presents with scaling, erythema, and maceration of interdigital spaces. Treatment involves topical or oral antifungal agents (e.g., terbinafine).
• Candidiasis: Caused by Candida species. Presents with erythematous plaques with satellite lesions in intertriginous areas. Treatment involves topical antifungal agents (e.g., clotrimazole) or oral agents (e.g., fluconazole) for severe cases.

Parasitic Skin Infections

• Scabies: Caused by Sarcoptes scabiei mites. Presents with pruritic, linear burrows, and papules. Treatment involves topical scabicides (e.g., permethrin) applied to the entire body.
• Pediculosis (Lice): Three types: head lice (Pediculus humanus capitis), body lice (Pediculus humanus corporis), and pubic lice (Pthirus pubis). Treatment involves topical pediculicides and removal of nits.

Common Clinical Presentations

• Furuncle (Boil): Deep infection of a hair follicle caused by Staphylococcus aureus. Presents as a painful, erythematous, fluctuant nodule. Treatment may include incision and drainage, warm compresses, and antibiotics.
• Carbuncle: Collection of interconnected furuncles. Presents with a larger, deep-seated, painful, and fluctuant mass. Treatment involves incision and drainage, warm compresses, and antibiotics.
• Fol