Pigmentation Disorders
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Direct answer
Vitiligo is an autoimmune destruction of epidermal melanocytes producing chalk-white, non-scaly patches with Koebner localisation, frequently associated with thyroid disease and pernicious anaemia, whereas albinism is an enzyme defect — tyrosinase-negative oculocutaneous albinism being the classic form — in which melanocytes are present in normal numbers but cannot synthesise melanin. The paired spotter terms that examinations trade on are ephelis (freckle: increased melanin, normal melanocyte number, sun-induced) versus lentigo (increased numbers of melanocytes, flat and persistent), and the systemic flags — café-au-lait macules naming neurofibromatosis 1, and acanthosis nigricans flagging insulin resistance or, in its malignant form, an internal adenocarcinoma classically of the stomach.
What you must remember
- Vitiligo: well-demarcated depigmented (not hypopigmented) macules — melanocytes are absent, destroyed by CD8 T cells; Koebner phenomenon at friction sites; segmental versus non-segmental types; associations — autoimmune thyroid disease, pernicious anaemia, type 1 diabetes, Addison disease.
- Vitiligo management framing: cosmetic camouflage, topical calcineurin inhibitors or corticosteroids, narrow-band ultraviolet B phototherapy for extensive disease; surgical melanocyte grafting for stable patches.
- Albinism: oculocutaneous albinism from mutations such as tyrosinase (OCA1) or OCA2; normal melanocyte count, no melanin; nystagmus, photophobia, foveal hypoplasia and high skin cancer risk in Indian sun.
- Ephelis versus lentigo: freckle — basal-layer melanin increase with normal melanocyte numbers, appears with sun and may fade; lentigo — proliferation of melanocytes along the basal layer, stable, solar lentigo on chronically sun-damaged skin.
- Café-au-lait macules: six or more lesions over 5 millimetres in a prepubertal child (over 15 millimetres post-pubertal) supports neurofibromatosis 1, especially with axillary freckling; NF1 gene on chromosome 17, NF2 on 22 — the pair examiners quote.
- Acanthosis nigricans: velvety, hyperpigmented flexural thickening; reflects insulin resistance in most cases (obesity, type 2 diabetes, drugs); the malignant form accompanies internal adenocarcinoma — classically gastric — and may precede the cancer.
- Addison disease pigmentation: diffuse bronzing with buccal and palmar crease pigmentation from elevated pro-opiomelanocortin-derived melanocyte-stimulating hormone activity alongside adrenocorticotrophic hormone; in Indian tuberculosis remains an important cause of primary adrenal failure.
- Melasma: symmetric centrofacial brown patches of pregnancy and oral contraceptive use, worsened by sun; melasma darkens with ultraviolet exposure unlike vitiligo which is stable-white.
Two white patches, two completely different diseases
A 24-year-old presents with gradually enlarging chalk-white patches around the mouth and on the dorsal hands, some rectangular patches exactly at the site of her watch strap. The whiteness is complete depigmentation — under the microscope no melanocytes remain in the affected basal layer, having been destroyed by an autoimmune T-cell attack; the watch-strap patches demonstrate Koebner phenomenon. Screen her for thyroid disease, pernicious anaemia and diabetes, because vitiligo travels with organ-specific autoimmunity. The social dimension deserves one honest sentence in any Indian answer: depigmented patches carry heavy stigma because they are mistaken for leprosy, and explaining the non-infectious nature of vitiligo is part of treatment — a counselling point national guidelines and vivas both recognise.
Contrast a child from birth with uniform milky-white skin, white hair and grey-blue irides who squints and has nystagmus in daylight: oculocutaneous albinism. His melanocytes are present in normal numbers but biochemically idle, so the problem is manufacturing, not staffing — and the clinical consequences follow from absent melanin everywhere: photophobia and reduced visual acuity from foveal hypoplasia, and skin that burns and develops squamous carcinomas in Indian sunlight without rigorous photoprotection. Vitiligo loses cells late and locally; albinism never had function globally — one sentence that fixes both.
Where students slip
Depigmented and hypopigmented are used as synonyms; vitiligo is depigmented (total melanin and melanocyte loss) while tinea versicolor and post-inflammatory changes are hypopigmented — the word choice itself earns the mark. Ephelis and lentigo are interchanged; the discriminating fact is melanocyte number, normal in the freckle and increased in lentigo. The malignant form of acanthosis nigricans is forgotten until too late in the answer — sudden, rapidly progressive flexural pigmentation in an adult without metabolic risk factors warrants a search for gastrointestinal malignancy, not a moisturiser.
Frequently asked questions
What is the basic defect in vitiligo?
Autoimmune destruction of epidermal melanocytes, producing completely depigmented macules; associated with thyroid disease, pernicious anaemia and other organ-specific autoimmune conditions.
How does albinism differ from vitiligo pathologically?
In albinism melanocytes are present in normal numbers but melanin synthesis is defective; in vitiligo the melanocytes themselves are destroyed.
Which pigmentation disorder shows the Koebner phenomenon?
Vitiligo — patches appear at sites of friction or trauma, such as waistbands and watch straps; psoriasis and lichen planus share the phenomenon.
What distinguishes an ephelis from a lentigo?
A freckle has increased melanin with normal melanocyte numbers and fades without sun; a lentigo has an increased number of melanocytes and persists.
How many café-au-lait macules suggest neurofibromatosis 1?
Six or more, over 5 millimetres in prepubertal children (over 15 millimetres after puberty), particularly with axillary or inguinal freckling.
Which internal malignancy is linked with malignant acanthosis nigricans?
Gastrointestinal adenocarcinoma, classically gastric; sudden flexural acanthosis in a non-obese adult prompts a malignancy search.