# Internal Medicine/Approach to Skin Disorders
## Introduction

The challenge of examining the skin
Skin examination is a complex process involving the observation and analysis of the skin's surface. This task presents several challenges, including the need to differentiate between normal and abnormal findings, distinguish significant from trivial observations, and integrate these findings into a meaningful diagnostic framework. Essentially, skin examination is a crucial aspect of clinical practice, as it provides valuable insights into a patient's health.
Visibility of the largest organ
One unique aspect of skin examination is that it involves the largest organ in the human body—the skin itself. The skin's accessibility offers both advantages and disadvantages to clinicians. On one hand, it doesn't require specialized equipment or invasive procedures, making it relatively straightforward to examine. On the other hand, the surface area of the skin is extensive, and the sheer variety of possible skin conditions can be overwhelming.
Complexity of skin examination
Skin examination becomes particularly challenging due to the potential for variability in skin conditions. Sometimes, even minor variations in color, texture, or shape can be significant indicators of underlying skin or systemic diseases. For example, distinguishing between a benign nevomelanocytic nevus and a potentially malignant melanoma can be a nuanced process, requiring a trained eye.
Use of descriptive terms
To aid in the interpretation of cutaneous lesions and formulate a differential diagnosis, dermatologists and healthcare professionals have developed a wide range of descriptive terms. These terms help standardize the language used to describe skin conditions. For instance, the presence of scaling papules is characteristic of conditions like psoriasis or atopic dermatitis, whereas hemorrhagic papules may suggest vasculitis or sepsis.

## Approach to the Patient

Assessing the patient before history
A systematic approach to skin examination typically involves assessing the patient's skin before delving into an extensive medical history. This method ensures that the entire surface area of the skin is thoroughly evaluated before any potential biases from historical information are introduced. Objective findings from the examination can then be correlated with relevant patient history.
Four basic features
A comprehensive skin examination relies on the observation and documentation of four basic features of skin issues:
* Distribution: Examining where on the body the skin lesions are located. This is often a critical clue for diagnosis. For instance, a generalized rash might suggest a systemic condition, while a rash localized to sun-exposed areas could indicate a different cause.
* Types of Primary and Secondary Lesions: Identifying the primary lesion (the initial skin change) and any secondary changes that have occurred as a result. Secondary changes include crust, scale, erosion, ulceration, or excoriation.
* Shape of Individual Lesions: Observing the shape and configuration of individual lesions. Some conditions present with specific lesion shapes, such as target-shaped lesions in erythema multiforme.
* Arrangement of Lesions: Understanding how the lesions are arranged in relation to each other. For example, linear arrangements may suggest external factors like contact dermatitis.
Comprehensive skin examination
A thorough skin examination encompasses more than just the skin's surface. It includes evaluating not only the skin itself but also the hair, nails, and mucous membranes. This comprehensive approach is essential because skin conditions can manifest in various ways across these different components. For example, certain skin conditions may affect both the skin and nails, providing crucial diagnostic clues.
Importance of distribution
Distribution is a key element in skin examination. The location of skin lesions can often provide valuable diagnostic insights. For instance, a patient with a generalized erythematous exanthem (widespread skin rash) is more likely to have a drug eruption when compared to a patient with a similar rash limited to specific areas of the face exposed to sunlight.
Distinguishing by primary lesion
Once the distribution of skin lesions is established, the next step involves determining the nature of the primary lesion. Primary skin lesions are the initial morphological changes in the skin that result from the disease process. Identifying the primary lesion is crucial in narrowing down potential diagnoses. For instance, if a patient presents with lesions on the elbows, knees, and scalp, the primary lesion's nature may point towards psoriasis or dermatitis herpetiformis.
Secondary changes in skin
In addition to primary lesions, healthcare professionals also pay close attention to secondary changes in the skin. These changes often occur as a result of the disease process or due to the patient's actions, such as scratching. Common secondary changes include the presence of scale (indicating excessive epidermal growth) or crust (resulting from a discontinuous epithelial cell layer). Recognizing these secondary changes can help refine the diagnosis further.
Palpation of skin lesions
Palpation, or the act of feeling the skin lesions, plays a critical role in skin examination. By gently pressing on or feeling the lesions, healthcare providers can gain additional information about their characteristics. For example, red papules on the lower extremities that blanch (become pale) when pressure is applied can be associated with various diseases. However, hemorrhagic red papules that do not blanch with pressure suggest palpable purpura, a distinctive feature of necrotizing vasculitis.
Shape and arrangement of lesions
The shape of individual lesions and their arrangement are essential aspects of skin examination. Identifying specific lesion shapes can be highly indicative of particular skin conditions. For instance, flat, round, erythematous papules and plaques are common in many skin diseases. However, target-shaped lesions that consist of erythematous plaques surrounded by a paler ring are specific to erythema multiforme.
Importance of arrangement
Furthermore, the arrangement of lesions provides valuable diagnostic clues. Lesions arranged in specific patterns, such as linear or grouped configurations, can suggest certain causes. For instance, erythematous papules and vesicles arranged linearly may indicate an external cause like allergic contact dermatitis, where the skin reacts to a specific allergen in a linear pattern. In contrast, generalized arrangements of lesions often point towards systemic conditions.

## Diagnostic Techniques

Diagnosing skin diseases
While many skin diseases can be identified based on their clinical appearance, there are instances where diagnostic procedures are necessary to confirm or clarify a diagnosis. These diagnostic techniques are often straightforward and can be performed at the patient's bedside with minimal equipment.

### Skin Biopsy

A straightforward procedure
Skin biopsy is a minor surgical procedure commonly used to obtain a tissue sample for diagnostic purposes. However, it's essential to choose the right lesion for biopsy to maximize the chances of obtaining diagnostic information. The decision on which lesion to biopsy may require expertise in dermatology and an understanding of superficial anatomical structures in specific areas of the body.

### KOH Preparation

Detecting fungal infections
A potassium hydroxide (KOH) preparation is a diagnostic technique used when a fungal infection is suspected, particularly in cases involving scaling skin lesions. The procedure involves gently scraping the edge of the lesion using a scalpel blade. The collected scale is then placed on a glass microscope slide and treated with a solution containing 10-20% KOH. This treatment dissolves keratin, a protein found in the epidermis, making it easier to visualize fungal elements under a microscope.
KOH preparation is valuable for identifying various fungal infections, including dermatophyte infections (where hyphae are observed), Candida infections (showing pseudohyphae and budding yeasts), and tinea versicolor (characterized by "spaghetti and meatballs" yeast forms).

### Tzanck Smear

Detecting herpesvirus infections
A Tzanck smear is a cytologic technique used primarily in the diagnosis of herpesvirus infections, such as herpes simplex virus (HSV) or varicella-zoster virus (VZV). The procedure involves unroofing an early vesicle (blister), not a pustule or crusted lesion, and gently scraping the base of the lesion with a scalpel blade. The collected material is placed on a glass slide, air-dried, and stained with Giemsa or Wright's stain.
Multinucleated epithelial giant cells observed in the smear suggest the presence of HSV or VZV. To identify the specific virus strain, further testing, such as culture, immunofluorescence microscopy, or genetic testing, is necessary.

### Diascopy

Distinguishing skin lesions
Diascopy is a technique used to assess whether a skin lesion blanches (becomes pale) with applied pressure. This method helps distinguish between different types of skin lesions. For example, urticaria (hives) typically blanches with pressure, while purpuric lesions caused by necrotizing vasculitis do not.
During diascopy, a microscope slide or magnifying lens is pressed against the lesion, and the amount of blanching that occurs is noted. Granulomas often have a distinctive appearance on diascopy, appearing opaque to transparent with a brown-pink "apple jelly" appearance.

### Dermoscopy

Noninvasive skin examination
Dermoscopy is a noninvasive method for examining the skin's surface. It involves using a high-quality magnifying lens and a specialized light source called a dermatoscope. Dermoscopy allows healthcare providers to identify skin structures, colors, and patterns that are not visible to the naked eye. This technique is particularly useful for evaluating pigmented skin lesions.

### Wood's Light

Use of ultraviolet light
A Wood's lamp emits 360-nm ultraviolet ("black") light, which aids in the evaluation of specific skin disorders. For example, erythrasma, a superficial infection caused by Corynebacterium minutissimum, appears coral pink under a Wood's lamp. Wounds colonized by Pseudomonas may appear pale blue, and certain dermatophytes, like Microsporum canis or M. audouinii, exhibit a yellow fluorescence.
Pigmented lesions on the epidermis, such as freckles, become more accentuated under a Wood's lamp. In contrast, dermal pigmentation, like postinflammatory hyperpigmentation, tends to fade under this light. Vitiligo, characterized by depigmentation due to melanocyte loss, appears completely white under a Wood's lamp. Additionally, a Wood's lamp can be used to detect tinea versicolor and identify ash leaf spots in patients with tuberous sclerosis.

### Patch Tests

Identifying sensitivity to antigens
Patch testing is a diagnostic procedure aimed at documenting an individual's sensitivity to specific antigens or allergens. This procedure involves applying a battery of suspected allergens to the patient's back under occlusive dressings. These dressings are left in place, in contact with the skin, for 48 hours. After removal, the area is examined for evidence of delayed hypersensitivity reactions, such as erythema (redness), edema (swelling), or papulovesicles (small, raised, fluid-filled lesions).
Patch testing is a specialized procedure typically performed by physicians with expertise in this area. It is especially valuable in the evaluation of patients with chronic dermatitis, as it can help pinpoint specific allergens or triggers responsible for the skin condition.

## Conclusion

Specialized diagnostic techniques
In conclusion, skin examination is a fundamental aspect of medical practice, providing valuable insights into a patient's health. While many skin conditions can be diagnosed based on clinical appearance, specialized diagnostic techniques play a crucial role in confirming or clarifying diagnoses. These techniques, such as skin biopsy, KOH preparation, Tzanck smear, diascopy, dermoscopy, Wood's light examination, and patch testing, are essential tools in the dermatologist's toolkit. They enable healthcare professionals to provide accurate diagnoses and develop effective treatment plans for patients with various skin disorders. The choice of diagnostic technique depends on the specific clinical presentation and suspected underlying causes of the skin condition.