# Internal Medicine/Cutaneous Infections
## Impetigo, Ecthyma, and Furunculosis

Impetigo is a common superficial bacterial skin infection primarily caused by Staphylococcus aureus and occasionally by group A β-hemolytic streptococci. The characteristic feature is the development of superficial pustules that rupture and form a characteristic honey-colored crust. These lesions can occur on healthy skin (primary infection) or in areas already affected by other skin conditions (secondary infection). Staphylococcal impetigo can sometimes manifest as bullous impetigo, where clear blisters form due to the production of exfoliative toxin. This toxin is also responsible for staphylococcal scalded-skin syndrome, which causes superficial epidermis loss due to blistering. Ecthyma is a deeper form of impetigo, often caused by Streptococcus pyogenes, leading to punched-out ulcerative lesions that heal with scarring. Treatment includes gentle debridement, topical antibiotics, and oral antibiotics as necessary.
Furunculosis is another condition caused by Staphylococcus aureus and has gained attention due to the emergence of community-associated MRSA (CA-MRSA). It presents as painful, erythematous nodules on the skin, commonly appearing in multiple lesions. Incision and drainage may be required for larger furuncles. It's important to culture lesional material whenever possible. Treatment for methicillin-sensitive infections involves β-lactam antibiotics, while CA-MRSA requires different approaches.

## Dermatophytosis

Dermatophytes are fungi that infect the skin, hair, and nails and include Trichophyton, Microsporum, and Epidermophyton genera. Tinea corporis affects the hairless skin of the body and appears as erythematous, scaly plaques, often forming ring-like patterns. Tinea cruris, commonly found in males, presents as a scaling, erythematous rash sparing the scrotum. Tinea pedis, the most prevalent dermatophyte infection, causes variable symptoms on the feet, including erythema, edema, scaling, pruritus, and vesiculation. Tinea unguium or onychomycosis occurs in many patients with tinea pedis and results in thickened, opaque nails. Scalp infection (tinea capitis) predominantly affects children, causing mild scale and hair loss. Diagnosis is based on clinical appearance and microscopic examination.
Treatment options depend on the infection site and type. Topical agents work well for uncomplicated tinea corporis, tinea cruris, and limited tinea pedis. Griseofulvin is approved for dermatophyte infections, but it has side effects like gastrointestinal distress and headache. Itraconazole and terbinafine are sometimes used off-label for certain infections but require caution due to potential drug interactions and side effects.

## Tinea (Pityriasis) Versicolor

Tinea versicolor, caused by Malassezia furfur, results in oval, scaly macules and patches, often found on the chest, shoulders, and back. Lesions can appear as hypopigmented areas on dark skin or slightly erythematous on light skin. A potassium hydroxide (KOH) preparation of lesions shows characteristic short hyphae and round spores, resembling "spaghetti and meatballs." Topical treatments like sulfur, salicylic acid, or selenium sulfide lotions or shampoos are the primary options and should be applied daily for a few weeks.

## Candidiasis

Candidiasis is a fungal infection typically caused by Candida albicans. It can affect the skin and mucous membranes and is common in individuals with predisposing factors like antibiotic therapy, diabetes, or immunosuppression. Oral candidiasis (thrush) appears as white plaques on the tongue or buccal mucosa. Perlèche presents as fissured, macerated lesions at the corners of the mouth. Cutaneous candidal infections are often seen in moist, macerated areas and involve erythematous, edematous, and scaly skin with scattered "satellite pustules." Diagnosis is based on clinical presentation and microscopic examination.
Treatment involves removing predisposing factors and using appropriate topical or systemic antifungal agents. Topical options include nystatin or azoles, and mild glucocorticoid creams can be used for associated inflammation. Systemic therapy is reserved for immunosuppressed or chronic cases, with oral fluconazole being an option for cutaneous candidiasis.

## Warts

Warts are skin neoplasms caused by human papillomaviruses (HPVs). They come in various forms, including verruca vulgaris, plantar warts, flat warts (verruca plana), and filiform warts. Genital warts are also caused by HPVs and can affect various genital and mucosal areas. Some HPVs are associated with an increased risk of cancer, such as cervical carcinoma.
Treatment of warts depends on factors like location, extent, patient age, and immune status. Cryotherapy with liquid nitrogen is effective for various warts. Keratolytic agents like salicylic acid can be used for nongenital warts. Podophyllin is an option for genital warts but can cause local reactions. Topical imiquimod is approved for genital warts. A vaccine for specific HPV types is available and reduces the risk of certain cancers associated with the virus.