Ichthyoses
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Direct answer
The ichthyoses are disorders of cornification producing generalised scaling, and the examinable map runs from common to catastrophic. Ichthyosis vulgaris, the commonest (autosomal dominant, filaggrin mutation), gives fine white scale sparing flexures, with hyperlinear palms and atopic association. X-linked recessive ichthyosis (steroid sulfatase deficiency) affects males with large, dark, "dirty" polygonal scale that involves the neck and flexures, plus cryptorchidism, corneal opacities and failure of labour onset from placental sulfatase deficiency. Autosomal recessive congenital ichthyosis presents as a collodion baby — a newborn encased in a shiny, taut membrane that fissures and sheds — evolving into lamellar ichthyosis (TGM1, plate-like scale, ectropion) or congenital ichthyosiform erythroderma. Epidermolytic ichthyosis (KRT1/KRT10) is born with blisters that give way to cobblestone hyperkeratosis, and harlequin ichthyosis (ABCA12) is the severe armour-plate disease. Acquired ichthyosis in an adult means a search for lymphoma, malignancy, HIV, hypothyroidism or drugs.
What you must remember
- Ichthyosis vulgaris: filaggrin, autosomal dominant; fine white scale on extensors with flexural sparing, hyperlinear palmar creases, keratosis pilaris, atopic diathesis; improves with age and humidity.
- X-linked recessive ichthyosis: steroid sulfatase (arylsulfatase C) deficiency; males; large dark polygonal scale, neck involvement (the "dirty neck"), flexures may be involved; cryptorchidism, comma-shaped corneal opacities, and maternal labour fails to progress (placental sulfatase) — a lovely obstetric crossover.
- Collodion baby: taut, cellophane membrane at birth — danger from trans-epidermal water loss, hypernatraemic dehydration, sepsis, temperature instability, and ectropion exposure; manage in a humidified incubator with emollients, aggressive barrier nursing and ophthalmic care; most evolve into lamellar ichthyosis or CIE, a minority self-improve.
- Lamellar ichthyosis (TGM1): autosomal recessive; plate-like, armour-like dark scale, ectropion, eclabium, no blisters; congenital ichthyosiform erythroderma is its erythrodermic sibling within ARCI.
- Epidermolytic ichthyosis (KRT1/KRT10): autosomal dominant; neonatal blisters and erosions evolve into cobblestone flexural and joint-flexion hyperkeratosis; histology of epidermolytic hyperkeratosis; blister-prone in heat — the "bullous ichthyosis" of older books.
- Harlequin ichthyosis (ABCA12): massive armour plates with deep fissures, severe ectropion and eclabium, restriction of breathing and feeding; modern neonatal intensive care with early oral retinoids has transformed survival.
- Syndromic one-liners: Sjögren-Larsson (fatty aldehyde dehydrogenase — ichthyosis with spastic diplegia and intellectual disability); Netherton (SPINK5 — bamboo hair/trichorrhexis invaginata, ichthyosis linearis circumflexa, atopy, hyper-IgE); Refsum (phytanic acid — retinitis pigmentosa, anosmia, ataxia); KID syndrome (GJB2 connexin 26).
- Acquired ichthyosis — the hidden cancer flag: new-onset generalised scaling in an adult without childhood history demands evaluation for lymphoma and other malignancies, HIV, hypothyroidism, sarcoidosis, and drugs (nicotinic acid, clofazimine, EGFR inhibitors).
- Therapy backbone: emollients and keratolytics (urea 10%, lactic acid 5-12%, salicylic acid — caution for salicylate toxicity over large areas in children), soak-and-smear technique, and oral acitretin for severe congenital forms with contraception counselling.
From the labour room to the emollient aisle
A newborn emerges sheathed in a glistening, cracking membrane, eyelids everted, lips pulled taut. The neonatology moves first: humidified incubator, sterile handling, emollients several times daily, fluids tuned to the enormous insensible losses, and ophthalmic lubrication for the ectropion. Over two weeks the collodion membrane desquamates; a small minority of such babies reveal normal skin underneath ("self-improving collodion baby"), but most declare their genotype — lamellar ichthyosis with dark plates, or CIE with erythroderma and finer scale. Genetics is drawn early; the parents are counselled about autosomal recessive recurrence.
Contrast the adult consultation: a 55-year-old develops fish-like scaling over the limbs in three months, no childhood history, no family history. This is acquired ichthyosis, and the correct next move is not the emollient shelf but the work-up — full blood count and smear, HIV and thyroid testing, chest imaging where indicated, and a drug review. Generalised pruritus with new ichthyosis in a middle-aged adult is one of dermatology's genuine malignancy alarms; the emollient is what you apply while the search proceeds.
Where the exam harvests its marks
Three axes generate most questions. Gene-matching: filaggrin — vulgaris; steroid sulfatase — X-linked recessive; TGM1 — lamellar; KRT1/10 — epidermolytic; ABCA12 — harlequin; SPINK5 — Netherton. Inheritance: autosomal dominant (vulgaris, epidermolytic) versus recessive (ARCI, harlequin) versus X-linked recessive. Clinical discriminators: flexural sparing (vulgaris), "dirty" scale with cryptorchidism (X-linked), blisters at birth (epidermolytic), ectropion with plate scale (lamellar), bamboo hair (Netherton). The collodion-baby stem tests management priorities, and the adult-onset stem expects malignancy and HIV screening among the options.
Frequently asked questions
Which gene is defective in ichthyosis vulgaris?
Filaggrin — autosomal dominant, producing fine white scale with flexural sparing, hyperlinear palms and an atopic tendency.
What endocrine-obstetric clue accompanies X-linked ichthyosis?
Failure of labour to progress, due to placental steroid sulfatase deficiency, alongside cryptorchidism and corneal opacities in the affected male.
How is a collodion baby managed in the nursery?
Humidified incubator, liberal emollients, meticulous infection control, fluid and electrolyte monitoring, and eye care for ectropion — while awaiting the underlying diagnosis.
Which ichthyosis presents with neonatal blisters?
Epidermolytic ichthyosis (KRT1/KRT10) — blisters and erosions at birth that later transform into cobblestone hyperkeratosis.
What must be excluded in adult-onset acquired ichthyosis?
Lymphoma and internal malignancy, HIV infection, hypothyroidism, sarcoidosis and drug causes — the skin may be the first sign of systemic disease.