What are the differential diagnoses for progressive depigmented to hypopigmented patches around the mouth, under the right eye, and on the neck (with small repigmented macules within the neck lesions and accentuation on Wood's lamp) in a mother/daughter pair (1‑year duration) and a father/son pair (4‑month duration)?

Vitiligo is the Most Likely Diagnosis

Based on the clinical presentation—progressive depigmented-to-hypopigmented patches in perioral, periocular, and neck regions with Wood's lamp accentuation and characteristic repigmentation macules—vitiligo is the primary diagnosis to consider, particularly given the familial clustering in two separate parent-child pairs. 1

Key Diagnostic Features Supporting Vitiligo

The presentation demonstrates classic vitiligo characteristics:

• Distribution pattern: Perioral, periocular, and neck involvement represents typical acrofacial vitiligo distribution, which commonly affects body orifices 1
• Wood's lamp findings: Accentuation of whitening under Wood's lamp is characteristic of true depigmentation from melanocyte loss 1
• Repigmentation macules: The presence of small repigmented macules within depigmented patches on the neck is pathognomonic for vitiligo—this "trichrome" appearance with intermediate pigmentation zones is specifically described in vitiligo 1
• Progressive course: Both families report progressive expansion (1 year and 4 months respectively), consistent with active vitiligo 1
• Familial clustering: The mother-daughter and father-son pattern strongly suggests genetic predisposition, as vitiligo shows familial traits in approximately 18% of cases 1

Critical Differential Diagnoses to Exclude

While vitiligo is most likely, systematically exclude these conditions 1:

High Priority Differentials:

Pityriasis alba:

• Would show fine scaling and less distinct borders
• Wood's lamp typically does NOT show marked accentuation
• More common in children but doesn't explain the parental involvement
• Lacks the characteristic repigmentation islands 2, 3

Progressive macular hypomelanosis (PMH):

• Presents as ill-defined hypopigmented (not depigmented) macules primarily on trunk
• Typically shows red follicular fluorescence under Wood's lamp (not white accentuation)
• Rarely extends to face/neck as primary sites 4
• The perioral and periocular distribution argues against this

Pityriasis versicolor:

• Would demonstrate fine scaling on scraping
• KOH preparation would show "spaghetti and meatballs" pattern
• Typically trunk-predominant
• Wood's lamp shows yellow-green fluorescence, not white accentuation 2, 3

Post-inflammatory hypopigmentation:

• Requires preceding inflammatory dermatosis
• No history of inflammation provided
• Bilateral symmetrical distribution without trauma history makes this unlikely 5

Lower Priority but Important Differentials:

Nevus depigmentosus:

• Present from birth or early infancy (not acquired)
• Non-progressive and stable
• The 4-month to 1-year progressive history excludes this 6, 3

Tuberous sclerosis (ash-leaf macules):

• Would require additional stigmata (seizures, developmental delay, cardiac rhabdomyomas)
• Ash-leaf macules typically present at birth
• Lack of systemic features makes this unlikely 6

Idiopathic guttate hypomelanosis:

• Presents as small (2-5mm) porcelain-white macules on sun-exposed extremities
• Typically in older adults
• Sharp margins with complete pigment network absence on dermoscopy
• Distribution doesn't match 2, 3

Diagnostic Approach

Immediate clinical assessment:

1. Confirm complete absence of scaling (rules out pityriasis versicolor and pityriasis alba)
2. Document bilateral symmetry and perioral/periocular distribution
3. Verify Wood's lamp shows stark white accentuation (not yellow-green or red fluorescence)
4. Examine for Koebner phenomenon at sites of trauma
5. Check for leukotrichia (white hairs within patches) 1

Laboratory evaluation:

• Thyroid function tests are mandatory: 34% of vitiligo patients have autoimmune thyroid disease 1
• Consider antithyroid antibodies
• Family history of autoimmune conditions (obtained in 32% of vitiligo patients) 1

Biopsy is NOT required when presentation is classical 1. The diagnosis can be made clinically in primary care for typical presentations 1.

Common Diagnostic Pitfalls

Critical errors to avoid:

1. Misdiagnosing pityriasis alba as vitiligo: Pityriasis alba shows hypopigmentation (not depigmentation), has indistinct borders, and shows minimal Wood's lamp enhancement 5, 2

2. Overlooking the repigmentation islands: These small pigmented macules within depigmented patches are virtually pathognomonic for vitiligo and should not be dismissed 1

3. Failing to screen for thyroid disease: This is a guideline-level recommendation given the high association 1

4. Premature labeling without certainty: As highlighted in recent literature, incorrectly diagnosing non-vitiliginous conditions as vitiligo carries significant psychosocial burden, particularly in children 5

Management Implications Based on Diagnosis

If vitiligo is confirmed (which is most likely):

For the children (daughter and son):

• Potent or very potent topical corticosteroids for trial period ≤2 months 1
• Topical tacrolimus or pimecrolimus preferred over steroids due to better safety profile in children (Grade B/1+) 1
• Narrowband UVB phototherapy reserved for widespread disease unresponsive to topical therapy 1
• Psychological counseling should be offered to both children and parents 1

For the parents (mother and father):

• Similar topical approach with potent steroids (≤2 months) or calcineurin inhibitors 1
• Consider narrowband UVB if widespread or significant quality of life impact 1
• Camouflage cosmetics and sunscreens as adjunctive measures 1

Surgical treatments are contraindicated in all four patients given the progressive nature (requires 12 months stability) 1

The familial pattern, characteristic distribution, Wood's lamp findings, and presence of repigmentation islands make vitiligo the definitive diagnosis requiring no further diagnostic workup beyond thyroid screening.