Ichthyosis vulgaris exists in two forms, acquired and hereditary. The most common form is the hereditary ichthyosis vulgaris. In the US, hereditary ichthyosis vulgaris affects approximately 1:300 live births. The incidence of acquired ichthyosis vulgaris is unknown.
Acquired ichthyosis vulgaris is an autosomal dominantly inherited condition. Autosomal inheritance refers to genes occurring on any chromosome but the X or Y sex linked chromosomes. Only one copy of the faulty gene is required for a person to exhibit the symptoms of a dominant condition. A recessive trait on the other hand would require the inheritance of the gene from both parents. Where a patient acquires the faulty gene from both parents (homozygous ichthyosis vulgaris), they exhibit a more severe form of the condition. Patients with a single gene (heterozygous ichthyosis vulgaris), may present with very mild form of the condition or possibly be asymptomatic.
The faulty gene in ichthyosis vulgaris is the profilaggrin gene. This gene leads to the protein filaggrin. The affect of this faulty gene is a build up and retention of keratin in the skin. Filaggrin is thought to play a role in water binding in the skin. Cycles of skin hydration and dehydration are important the desquamation of the upper layers of the skin.
Ichthyosis vulgaris presents as scaly skin predominantly on the legs although it may appear elsewhere. The scales may be small (1 mm) and fine or large (1 cm) and thick depending on the severity of the condition. On the shins, the scales are thicker and darker than those seen elsewhere on the body, often they appear in a mosaic pattern. The name ichthyosis derives from the Greek word ichthys meaning fish and refers to the appearance of the skin scales in severe cases.
Babies with hereditary ichthyosis vulgaris rarely show symptoms at birth. The symptoms usually appear between the ages of one and five years old. Symptoms of hereditary ichthyosis vulgaris get progressively worse as the child reaches puberty after which they moderate and may disappear. Some patients exhibit spiny papules (keratosis pilaris or follicular hyperkeratosis) on the neck, cheeks or the back of the arms. Dry scaling skin covers the scalp of some patients.
A number of patients with hereditary ichthyosis vulgaris haves other associated conditions. Included amongst such conditions are eczema, hay fever and asthma.
Symptoms appear worse in the winter and in people living in colder climates.
Acquired ichthyosis vulgaris generally appears in adults. It is an indication of an underlying systemic condition. Conditions associated with acquired ichthyosis vulgaris include cancer, thyroid disease, HIV, leprosy and renal failure. Some drugs cause as a side effect of their usage in some patients. These drugs are nicotinic acid, triparanol, butyrophenones, dixyrazine, cimetidine, and clofazimine.
Another rare form of ichthyosis vulgaris, known as bathing suit ichthyosis vulgaris, is an autosomal recessive disorder. This requires the inheriting of the faulty gene from both parents. Unlike hereditary ichthyosis vulgaris the scaly skin occurs on area covered by the by a bathing suit and not on the extremities. This form of the condition relates to a transglutaminase-1 deficiency.
Treatments for ichthyosis vulgaris include retinoids such as tretinoin (Retin-A, Avita) or tazarotene (Tazorac), which decrease the action of the hyperactive keratin producing cells in the skin. Creams to increase the moisture in the skin such as Ammonium lactate (Lac-Hydrin) also help in easing the symptoms. Patients with acquired ichthyosis vulgaris tend to improve with treatment of their underlying condition.
Some patients experience an irritation causing them to scratch the skin . This sometimes results in a secondary bacterial infection, which requires antibiotic therapy.