Lesson 10.4: Skin Infections and Skin Cancer

Introduction

Skin infections and skin cancer represent significant areas of public health concern, particularly in the realm of ambulatory medicine. This lesson will dissect various types of skin infections—bacterial, viral, and fungal—while also exploring skin cancer, including premalignant lesions and the two major categories of skin cancer: melanoma and nonmelanoma. The objectives of this lesson are to help students (all caps) understand common skin infections, how to diagnose and manage them effectively, recognize necrotizing infections, and triage suspicious skin lesions.

Skin Infections

Skin infections are caused by various pathogens, each presenting unique characteristics and requiring different treatment approaches. The main categories include bacterial, viral, and fungal infections, with special emphasis on necrotizing infections, which are emergency conditions.

1. Bacterial Skin Infections

Bacterial skin infections are caused by pathogens like Staphylococcus aureus, Streptococcus pyogenes, and others. These infections can range from mild to severe, with the latter potentially leading to systemic illness.

Common Bacterial Infections:

Impetigo: A highly contagious skin infection characterized by vesicles and honey-colored crusts. It commonly affects children. Treatment typically includes topical antibiotics such as fusidic acid or mupirocin.

Example: A child presents with sore and crusty lesions around the mouth. On examination, vesicles are noted. The clinician prescribes a topical antibiotic.

Folliculitis: An infection of hair follicles often resulting in pus-filled bumps surrounding the follicles. Mild cases can be treated with warm compresses and antiseptics, while moderate cases might require antibiotics.

Cellulitis: A deeper skin infection characterized by redness, swelling, and pain. Depending on severity, treatment may involve oral or intravenous antibiotics.

Necrotizing Fasciitis

Necrotizing fasciitis (NF) is a life-threatening condition characterized by rapid tissue necrosis and systemic toxicity. It can result from various bacteria, including group A Streptococcus and mixed flora.

Diagnosis: Rapid clinical assessment is crucial. Look for signs of severe pain, fever, and systemic instability. Imaging studies (such as CT or MRI) may assist in determining the extent of the infection.

Example: A patient presents with severe leg pain, fever, and swelling. Initial imaging shows fascial edema. Immediate surgical intervention is required.

2. Viral Skin Infections

Viral infections are numerous, with the most common being herpes simplex virus (HSV), varicella-zoster virus (VZV), and human papillomavirus (HPV).

Key Viral Infections:

Herpes Simplex Virus: HSV can present as painful vesicular lesions on the lips (HSV type 1) or genital region (HSV type 2). Antivirals like acyclovir can shorten the duration of outbreaks.

Example: A patient develops painful, vesicular lesions on the lip. Acyclovir is initiated, and the healing process accelerates.

Varicella (Chickenpox): Characterized by a vesicular rash that progresses through stages from macules to pustules. Vaccination has significantly reduced incidence.

Human Papillomavirus: Certain HPV strains lead to common warts (verrucae vulgaris), while others can cause genital warts. Treatments include cryotherapy, topical acids, or surgical removal.

3. Fungal Skin Infections

Fungal skin infections, or dermatophytoses, typically present as itchy, red, scaly patches. The most common causes are dermatophytes and yeasts.

Common Fungal Infections:

Tinea (Ringworm): Caused by dermatophytes, presenting as circular erythematous patches with clear centers. Treatment includes topical or oral antifungals.

Candidiasis: Typically presents as red, itchy patches that may develop in moist areas such as armpits and groin. Treatment includes azole antifungals.

Skin Cancer

Skin cancer is the most common form of cancer in the United States, with two main categories: melanoma and nonmelanoma skin cancers.

1. Nonmelanoma Skin Cancer

Nonmelanoma skin cancers include basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). These cancers are typically localized and have a high cure rate when detected early.

Basal Cell Carcinoma (BCC)

Characteristics: Often appears as a painless, pearly nodular lesion, though it can take other forms. BCC rarely metastasizes but can cause local destruction.

Example: A patient presents with a slow-growing bump on the nose, which is excised and confirmed as BCC.

Squamous Cell Carcinoma (SCC)

Characteristics: Can arise from actinic keratosis and presents as a scaly red patch or ulcerated lesion. Early detection is crucial to prevent metastasis.

2. Melanoma

Melanoma is a malignant tumor arising from melanocytes and is known for its aggressive behavior. It can metastasize quickly, making early detection vital.

Characteristics of Melanoma

The ABCDE criteria help in assessing moles for potential malignancy:

Asymmetry: One half is different from the other.
Border: Irregular, scalloped, or poorly defined edges.
Color: Non-uniform color (various shades of brown, tan, or black).
Diameter: Larger than 6 mm, although melanomas can be smaller.
Evolving: Changing shape, size, or color over time.

Example: A patient has a 7 mm irregularly shaped mole on the back that has changed in color over 3 months. A biopsy confirms melanoma.

Conclusion

In this lesson, students has gained an understanding of various skin infections, including the causes, symptoms, diagnostics, and management strategies. Additionally, the differences between benign skin lesions and malignancies such as melanoma and nonmelanoma skin cancers have been explored, along with effective approaches to diagnosis and treatment.

Study Notes

Skin infections are categorized as bacterial, viral, and fungal.
Necrotizing infections are surgical emergencies.
Melanoma can be identified using the ABCDE criteria.
Treatment for bacterial infections often involves antibiotics, while fungal infections require antifungals.
Early diagnosis and management are critical for skin cancers to ensure favorable outcomes.