Disorders of keratinisation

Learning objectives
Lichenoid diseases
Ichthyosis
Keratosis pilaris
Pityriasis rubra pilaris
Darier’s disease
Activity

Learning objectives

Describe common features of lichen planus, lichen sclerosus, ichthyosis, pityriasis rubra pilaris, Darier's disease and keratosis pilaris

Lichenoid diseases

Many skin diseases include the term ‘lichen’, which is thought to originate from a resemblance to the lichen that is found on trees.

Idiopathic lichen planus
Erosive lichen planus
Lichenoid drug eruption
Lichen sclerosus

Lichen simplex is a type of eczema and was discussed in the dermatitis section of this course. There are several other uncommon “lichen” conditions that will not be considered in this course.

Lichenoid histology refers to liquefaction degeneration of basal layer, dermal infiltration of inflammatory cells hugging the basal layer, colloid bodies (degenerating keratinocytes) and dermal melanin.

Lichenoid histology
Low power view	Liquefaction degeneration

Idiopathic lichen planus has the following features:

An occasional association with primary biliary cirrhosis, hepatitis-C and perhaps other liver diseases
Polygonal papules and plaques on ventral wrists, forearms and legs
Lacy pattern of white marks on buccal mucosa &/or genitals
Variable itching
Koebnerisation (lichen planus arising in areas of minor skin trauma such as excoriation)
Nail dystrophy (uncommon)

Follicular lichen planus (lichen planopilaris) results in perifollicular erythema and scaling in the scalp and other hair bearing areas. It may or may not arise in association with non-follicular or mucosal disease.

Lichen planus
The ventral wrist is a typical site	The shins is a common site	Hypertrophic lichen planus
Lacy-pattern in buccal mucosa	Nail dystrophy	Polygonal papules and plaques. Note white streaks (Wickham’s striae)

Treatment of lichen planus may include:

Potent topical steroids
Systemic steroids
Sometimes, immune suppressive agents or retinoids.

Erosive lichen planus affects the oral and/or genital mucosa. It may result in very painful ulceration and scarring.

Erosive lichen planus

Lichenoid drug eruption has similar histology, and sometimes clinical appearance. More often there is a diffuse eruption of mildly irritable flat dry patches on trunk and limbs. Common causes include thiazides, anti-malarials, gold and ACE inhibitors.

Chronic graft-versus-host disease (GVHD) also has lichenoid histology. Arising more than 100 days after bone marrow transplantation, there are lichen planus-like papules and dermal sclerosis.

Lichen sclerosus is a common cause of vulval itching and soreness in menopausal women. Only ten percent of cases affect other sites or men. It is thought to have an autoimmune origin, with an extracellular matrix protein as antigen. On the vulva, perineum and perianal mucosa, it causes white plaques, atrophy, sclerosis (scarring), haemorrhage, blistering and ulceration. In children, it is often confused with the results of sexual abuse.

Lichen sclerosus
Axillary lichen sclerosus	Penile lichen sclerosus (balanitis xerotica obliterans)	Vulval lichen sclerosus in pre-pubertal child
Extensive vulval, perineal and perianal disease	Hypertrophic lichen sclerosis	Perianal squamous cell carcinoma

Patients with lichen sclerosus should be under the care of a dermatologist. Ultrapotent topical steroids are generally successful but should be used with caution because of potential adverse effects.

Ichthyosis

Ichthyosis refers to a group of disorders of keratinisation characterised by excessively dry and scaly skin (abnormal differentiation and desquamation of the epidermis). Genetic analysis is identifying the protein abnormality responsible in specific subtypes.

The most common types of ichthyosis are:

Autosomal dominant ichthyosis vulgaris

The most common type (1:250)
Histology: absent granular layer
Most severe in childhood but may persist in adult life
Predisposes to atopic dermatitis
Generalised dryness most prominent on upper arms
May have hyperlinear palms

Autosomal recessive lamellar ichthyosis

Collodion baby (neonate encased in a membrane)
Extensive scaling on erythematous base
Mutation in gene coding for glutaminase (and other mutations)

X-linked recessive ichthyosis

Deficiency of steroid sulphatase in affected child and carrier mother
Large scales on trunk and limbs
Flexures may be spared

Bullous ichthyosiform erythroderma

Blistering and erythematous skin in infants
Prominent scaling on erythematous base in adults
Autosomal dominant mutation in keratin 1 & 10

Acquired ichthyosis is the dry skin associated with cachexia and certain forms of cancer and lymphoma. It is also characteristic in heavy consumers of kava.

Ichthyosis
Ichthyosis vulgaris	X-linked ichthyosis	Hyperlinear palms in ichthyosis vulgaris
Bullous ichthyosiform erythroderma	Bullous ichthyosiform erythroderma	Acquired ichthyosis in kava drinker

Treatment of ichthyosis requires regular application of emollients containing urea and/or lactic acid and the use of soap substitutes when bathing. Oral retinoids may be prescribed for severe cases.

Keratosis pilaris

Keratosis pilaris affects up to 50% of adolescents and may present from neonate to middle-age.

Common sites are outer aspect of upper arms and anterior thighs
The rough skin is due to follicular plugs of keratin
May result in non-pruritic erythema (keratosis rubra pilaris)
Rarely causes loss of the lateral eyebrows (ulerythema oophyrogenes)
May cause red dry cheeks (keratosis pilaris faciei)

Keratosis pilaris
Keratosis rubra pilaris	Keratosis pilaris faciei	Follicular plugging

Keratosis pilaris rarely clears with treatment. Urea-containing emollients may soften the affected areas. Topical retinoids encourage normal follicular keratinisation with improvement in the appearance in some patients but may irritate.

Pityriasis rubra pilaris

Pityriasis rubra pilaris (PRP) is the name given to a group of rare skin disorders resulting in localised erythematous scaly plaques rather like psoriasis. However there is less scaling and prominent follicular involvement. Keratoderma of palms and soles is usual. Both juvenile and adult types may result in erythroderma.

Pityriasis rubra pilaris
Juvenile PRP	Palmar keratoderma	Follicular papules

Darier’s disease

An uncommon inherited disorder with disordered keratinisation, resulting in characteristic greasy reddish papules in scalp and trunk, palmar pitting and nail changes. The onset of skin lesions is generally during adolescence. Darier's may be complicated by sunburn, staphylococcal infection, and herpes simplex virus infection