Diascopy in Dermatology: Mechanism of Action, Technique, and Differential Diagnosis of Skin Lesions

Diascopy is a simple yet informative diagnostic method in dermatology, based on the examination of skin changes under pressure. This technique is still used in modern dermatology due to its high diagnostic effectiveness and accessibility. Diascopy was first described in the late 19th century and remains in clinical use today.

Principle and Mechanism of Diascopy

Diascopy is performed by applying light pressure to the skin surface with a transparent glass or plastic spatula. For this purpose, a diascopic device with illumination or a dermatoscope may also be utilized. The procedure is based on the phenomenon of optical clearing of the epidermis under compression, which allows the healthcare professional to visually determine the nature of morphological elements, specifically:

• To differentiate hemorrhagic (bleeding) from erythematous (inflammatory) lesions.
• To detect hidden pigmentation.
• To assess vascular structures.

Step-by-Step Technique of Skin Diascopy

Diascopy is performed in several steps:

1. Preparation: the skin area to be examined is cleaned.
2. Application: the diascopic instrument is pressed firmly against the area until the surrounding tissues blanch.
3. Evaluation: changes in skin elements under pressure are assessed.
4. Revascularization: the time required for color restoration after pressure is recorded.
5. Interpretation: the results are analyzed.

Evaluation of Results: Positive and Negative Diascopy

The changes observed under pressure are differentiated into:

• Positive diascopy: the lesion disappears or changes its color (typical for vascular and inflammatory lesions).

• Negative Diascopy: no change in color is observed (typical for hemorrhagic and certain pigmented lesions).

Differential Diagnosis in Dermatology

Vascular Lesions

• Eczema, dermatitis: due to their inflammatory nature, the lesions tend to blanch under pressure and immediately regain color.
• Vasculitis: lesions do not disappear, as they are caused by hemorrhage.
• Telangiectasias: these lesions may blanch slightly but retain their distinct vascular pattern.
• Hemangiomas: upon examination, these elements blanch, then slowly regain color.

Pigmented Skin Lesions

• Dermal nevi: color remains unchanged.
• Melanoma: uneven pigmentation and abnormal color persist.
• Dermatofibroma: the pigment may blanch slightly; the “dimple sign” is observed.
• Hemosiderosis: lesion color intensity diminishes.

Infectious and Inflammatory Diseases

• Lupus vulgaris, sarcoidosis: the “apple jelly” sign is observed, with yellow-brown nodules visible.
• Granuloma annulare: firm papules blanch slightly.
• Roseola (in syphilis, toxicoderma, rubella, measles, typhus or typhoid fever): lesions disappear under pressure.

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Advantages and Limitations of Diascopy

Advantages

• The technique requires minimal time.
• It is completely safe and painless.
• No specific patient preparation is needed.
• The method does not require complex or expensive instruments.

Limitations

• Diascopy does not replace histological examination.
• The method has low informative value for deep-seated lesions.
• It requires extensive expertise for correct interpretation.