Key Takeaways
- Wood’s lamp: vitiligo shows bright chalk/blue-white accentuation with sharp borders; low-contrast off-white or coppery/yellow fluorescence suggests alternatives.
- Dermoscopy: absent pigment network with perifollicular brown dots/halos = early repigmentation (vitiligo); white scale points to tinea/pityriasis alba.
- History & distribution (onset in childhood, friction sites, chemical exposures, solitary since birth) often solve the puzzle without biopsy.
- Biopsy for atypical, inflammatory, indurated, or therapy-resistant patches—rule out hypopigmented mycosis fungoides and morphea/lichen sclerosus.
Fast Differential Algorithm
- Is it sharply depigmented under Wood’s lamp? If yes → vitiligo likely; if low-contrast or colored fluorescence → consider mimickers.
- Scale present? If yes → tinea versicolor or pityriasis alba (do KOH or emollient trial).
- Since birth/early childhood and stable? Nevus depigmentosus/achromic nevus.
- Small, drop-like on sun-exposed older skin? Idiopathic guttate hypomelanosis.
- Induration/atrophy or genital/perineal plaques? Lichen sclerosus/morphea → consider biopsy.
- Occupational/chemical exposure with splatter pattern? Chemical leukoderma—remove trigger.
- Pruritus, fine scale, trunk distribution? Tinea versicolor or pityriasis alba.
Look-Alikes: Quick Comparison Table
| Condition | Clues (Hx/Exam) | Wood’s lamp | Dermoscopy | Notes/Treatment hint |
|---|---|---|---|---|
| Post-inflammatory hypopigmentation (PIH) | History of rash/eczema/trauma at site; partial pigment loss | Low contrast, not bright chalk white | Hypopigmented network, background scale if eczematous | Emollients, anti-inflammatory care; repigmentation over months |
| Tinea versicolor | Fine scale; trunk; pruritus possible | Yellow-gold/coppery glow | Superficial white scale accentuated by scraping | Topical azoles/selenium; KOH if uncertain |
| Pityriasis alba | Children/atopic; cheeks; dry pale patches | Low contrast | Fine scale; reduced network | Emollients ± mild steroid; sun protection |
| Nevus depigmentosus | Since birth/childhood; stable; serrated borders | Less bright; segment stable | Hypopigmented network without active rim | Diagnosis is clinical; no progression |
| Idiopathic guttate hypomelanosis | Older adults; 2–5 mm macules on shins/forearms | Variable, small spots | Sharply demarcated pale dots | Benign; reassurance ± cosmetic options |
| Lichen sclerosus | Genital/perineal plaques, atrophy, pruritus | Pale/ivory; not chalk-white | Porcelain white with telangiectasia; follicular plugs | High-potency steroids; biopsy if atypical |
| Morphea (localized scleroderma) | Indurated plaques, lilac ring; trunk/limbs | Non-specific | White areas with linear vessels, peau d’orange | Biopsy if suspected; rheum/derm co-manage |
| Chemical leukoderma | Phenols/catechols; occupational; splash pattern | Bright but exposure-mapped | Similar to vitiligo at rim | Remove trigger; protective equipment; slow recovery |
| Hypopigmented mycosis fungoides | Persistent, pruritic, ill-defined patches; adolescents/young adults | Non-specific | Fine scale, dotted vessels; variable | Biopsy if persistent/atypical; oncology/derm follow-up |
| Oculocutaneous albinism | Generalized hypopigmentation, nystagmus, photophobia | Diffuse effect | Global pigment reduction | Genetics/ophthalmology referral |
Wood’s Lamp & Dermoscopy Pearls
- Vitiligo under Wood’s lamp: bright chalk/blue-white with sharp delineation; confetti flecks at rim imply activity.
- Perifollicular brown dots/halos on dermoscopy = early repigmentation islands (favorable sign).
- Scale changes the game: any visible scale → think infection/eczema; scrape to highlight scale and reconsider differential.
When to Biopsy / Refer
- Induration, atrophy, telangiectasia, or lilac ring (suspect morphea/lichen sclerosus).
- Persistent, pruritic patches with atypical borders or failure to respond to standard therapy (rule out hypopigmented MF).
- Solitary, evolving lesion with inflammation or pain.
- Unclear diagnosis after full exam with Wood’s lamp/dermoscopy.