vitiligo gold stand test
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Here is a complete, textbook-sourced answer on the gold standard diagnostic test for vitiligo:
Vitiligo: Gold Standard Diagnostic Test
Primary Answer: Wood's Lamp Examination
Wood's lamp (ultraviolet A light at 365 nm, used in a darkened room) is considered the gold standard clinical test for vitiligo. When shone on affected skin, it causes vitiligo patches to fluoresce as chalk-white or bright blue-white, sharply enhancing the contrast between depigmented and normally pigmented skin. This is especially useful in:
- Patients with lighter skin tones, where patches may be barely visible in normal light
- Distinguishing true depigmentation (complete melanocyte loss, as in vitiligo) from hypopigmentation (partial melanocyte loss, as in pityriasis alba, ash-leaf macules, tinea versicolor)
"Wood lamp examination in a dark room is helpful in differentiating the depigmentation of vitiligo from hypopigmentation seen in other diseases."
- Fitzpatrick's Dermatology, Vol 1&2
Why Wood's Lamp is Preferred
| Feature | Details |
|---|---|
| Non-invasive | No biopsy or blood draw required |
| Bedside test | Immediate results in the clinic |
| Differentiates depigmentation vs. hypopigmentation | Only complete melanocyte loss (vitiligo) gives chalk-white fluorescence |
| Helps in differential diagnosis | Tinea versicolor gives yellow-green fluorescence; pityriasis alba does not fluoresce brightly |
Histology (Confirmatory, Not Routine)
When the diagnosis is clinically straightforward, no biopsy is needed. However, if the presentation is atypical, skin biopsy is confirmatory:
- Shows complete absence of melanocytes in the epidermis (confirmed by immunohistochemistry with MART-1 or Melan-A staining)
- An active lesional border may show CD4+ and CD8+ T-cell interface infiltrate, with CD8+ T cells predominating in the epidermis
- This reflects the autoimmune destruction of melanocytes
"When the history and physical examination are consistent with vitiligo, there is usually no need for skin biopsy to confirm the diagnosis."
- Fitzpatrick's Dermatology, Vol 1&2
Summary Table
| Test | Role | Status |
|---|---|---|
| Wood's lamp examination | Primary clinical diagnostic tool | Gold standard |
| Skin biopsy + IHC (Melan-A/MART-1) | Confirms absent melanocytes histologically | Confirmatory (for atypical cases) |
| TSH / thyroid antibodies | Screens for associated autoimmune thyroid disease | Ancillary |
| Dermoscopy | Assesses borders, disease activity | Supplementary |
| ANA, CBC | Screens for other autoimmune associations | Ancillary |
Clinical Diagnosis Recap
Vitiligo is fundamentally a clinical diagnosis based on:
- Well-defined, chalky-white depigmented patches, often symmetrical
- Preference for periorificial (around eyes, mouth), acral, and genital areas
- Koebner phenomenon (new lesions at trauma sites)
- Wood's lamp confirmation of complete depigmentation
- Associated signs: halo nevi, poliosis (white hairs within patches)
Sources: Fitzpatrick's Dermatology, Vol 1&2 | Dermatology 2-Volume Set, 5th ed. (Bologna)
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Here is the complete differential diagnosis of vitiligo, directly from Fitzpatrick's Dermatology (the authoritative source):
Differential Diagnosis of Vitiligo
The key principle: Vitiligo causes true depigmentation (complete melanocyte loss). Most mimics cause only hypopigmentation (partial loss). Wood's lamp best separates the two.
1. Inherited / Congenital Hypomelanoses
| Condition | Key Distinguishing Features |
|---|---|
| Piebaldism (KIT mutation) | White forelock, midline anterior body + bilateral shin depigmentation - present at birth; autosomal dominant |
| Waardenburg syndrome (PAX3 mutation) | White forelock, heterochromic irides, deafness, hypertelorism; ± Hirschsprung disease |
| Tuberous sclerosis (TSC1/TSC2) | Ash-leaf macules (hypopigmented, not depigmented); seizures, angiofibromas, shagreen patch |
| Ito hypomelanosis | Hypopigmented macules along Blaschko lines; develops within first 2 years; chromosomal mosaicism |
| Nevus depigmentosus | Usually congenital, stable, grows proportionally with child; hypopigmented (not fully depigmented); jagged borders |
| Nevus anemicus | White macule present at birth; disappears with diascopy (pressure); no Wood's lamp accentuation |
2. Infectious Disorders
| Condition | Key Distinguishing Features |
|---|---|
| Tinea versicolor (Malassezia) | Fine scale; sebaceous areas (chest/back); yellow-green fluorescence on Wood's lamp (not chalk-white) |
| Leprosy (tuberculoid/borderline) | Hypopigmented patches with localized anesthesia (loss of sensation); nerve thickening |
| Treponematoses (syphilis, pinta) | Post-inflammatory hypopigmented patches; positive serology (RPR/TPHA) |
3. Post-inflammatory Hypopigmentation
| Condition | Key Distinguishing Features |
|---|---|
| Pityriasis alba | Ill-defined, mildly scaly, hypopigmented (not depigmented); common in atopic children; face predominance |
| Discoid lupus erythematosus | Scarring, follicular plugging, erythema, history of preceding inflammation |
| Psoriasis | Scale, Auspitz sign, nail pitting, history of psoriatic plaques |
| Lichen sclerosus et atrophicus | Atrophic, porcelain-white with wrinkling; genital predilection; secondary changes present |
| Scleroderma | Skin tightening, sclerodactyly, Raynaud's; systemic features |
| Chronic actinic dermatitis | Vitiligo-like depigmentation only after severe chronic course |
4. Para-malignant / Neoplastic
| Condition | Key Distinguishing Features |
|---|---|
| Mycosis fungoides (hypopigmented type) | Irregular hypopigmented patches on non-sun-exposed areas; atrophic epidermis; biopsy shows epidermotropism of atypical lymphocytes |
| Cutaneous melanoma | May have surrounding depigmentation (halo); histology shows atypical melanocytes |
5. Other Important Differentials
| Condition | Key Distinguishing Features |
|---|---|
| Chemical leukoderma | History of exposure to phenolic compounds (rubber, adhesives); occupational history; can mimic vitiligo exactly |
| Halo nevus | Depigmented ring around a central melanocytic nevus |
| Idiopathic guttate hypomelanosis | Small hypopigmented macules on sun-exposed areas in older patients; age-related |
Quick Wood's Lamp Summary
| Condition | Wood's Lamp Finding |
|---|---|
| Vitiligo | Chalk-white / bright blue-white fluorescence |
| Tinea versicolor | Yellow-green |
| Tuberous sclerosis ash-leaf | Faint enhancement (hypopigmented) |
| Pityriasis alba | Faint or no fluorescence |
| Nevus anemicus | No accentuation |
Source: Fitzpatrick's Dermatology, Vol. 1&2, Tables 76-1 and 76-2
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