How is vitiligo diagnosed?

Vitiligo is an autoimmune disease characterised by the selective loss of melanocytes and the emergence of white patches, and sometimes white hairs, on the skin's surface. Its diagnosis is generally quite straightforward and made clinically, that is, by observing the symptoms: skin depigmentation is indeed often visible to the naked eye. The use of a biopsy, a sample of tissue taken for analysis, is rare and is often only performed in cases of doubt, to rule out other disorders.

The diagnosis of vitiligo can be facilitated by the use of a Wood's lamp, an irradiation device that emits long UVA and violet-blue light. It allows for the identification of focal loss of melanocytes and the detection of depigmentation areas that may not be visible to the naked eye, particularly in individuals with very pale skin. In the depigmented lesions of vitiligo, the absence of melanocytes results in a lack of absorption of Wood's light by the epidermal melanin, causing most of the light to be reflected and the macules to emit a bright blue-white fluorescence and appear sharply delineated. This examination can also reveal blurred contours or confetti-like depigmentations, which indicate a high activity of the disease.

The Wood's lamp also aids in distinguishing vitiligo from other pathologies that can cause hypopigmentation, resulting in skin lightening, such as eczema or psoriasis. Indeed, many disorders can mimic vitiligo, particularly when it is at an early stage. A common clinical approach is to classify them based on the extent of the lesions, their pattern, and the degree of pigment loss. Further clinical differentiation can be made based on certain morphological signs, such as changes in the epidermis or dermis, like scaling or atrophy for example. The diagram below highlights some clinical signs that help establish the differential diagnosis of vitiligo.

It is also beneficial for the patient and the dermatologist to assess the severity of the vitiligo, in order to better anticipate its future progression. For this, there are several tools available, including:

• The BSA (Body Surface Area Index, Affected Body Surface).

  The BSA is a tool that indicates the percentage of skin surface presenting with vitiligo. In order to calculate it, the surface of the hand is considered to correspond to 1% of the total body surface. The specialist then assesses the number of "hands" corresponding to the surface of the lesions. Japanese guidelines classify the severity of vitiligo based on the percentage of the affected surface: less than 10% is considered mild, between 10 and 30%, vitiligo is moderate, and it is severe if the BSA exceeds 30%.

• The VASI (Vitiligo Area Severity Index, Severity Index of the Vitiligo Zone).

  The VASI is based on the assessment of six main body areas (head, upper trunk, lower trunk, arms, legs, and hands/feet), each being scored according to the percentage of surface area affected. This percentage is multiplied by the degree of observed depigmentation, which can range from 0, corresponding to no depigmentation, to 1, indicating complete depigmentation. The VASI score is considered an accurate method for measuring the progression of vitiligo as well as the effectiveness of treatments.

• The VES (Vitiligo Extent Score, Vitiligo Extent Score).

  The VES provides a simplified approach compared to the VASI and is based on the clinical recognition of depigmentation patterns that may be present across the entire body. It allows each patient to be assigned a severity level based on the extent of the depigmented areas, enabling a rapid assessment of the disease's severity. A variant of the VES, called the SA-VES (Self-Assessment VES), allows patients to carry out their own assessment of their dermatosis.

Once the diagnosis of vitiligo is established, it is important for the patient to follow the treatment(s) prescribed by the healthcare professional.

• KHOPKAR U. & al. The utility of dermoscopy in the diagnosis of evolving lesions of vitiligo. Indian Journal of Dermatology, Venereology, and Leprology (2014).

• PANDYA A. & al. Presentations, Signs of Activity, and Differential Diagnosis of Vitiligo. Dermatologic Clinics (2017).

• EZZEDINE K. & al. Vitiligo: A Review. Dermatology (2020).

• TANEW A. & al. S1 Guideline: Diagnosis and therapy of vitiligo. Journal der Deutschen Dermatologischen Gesellschaft (2022).