Approach
The term ichthyosis is a descriptive term that defines a particular type of scaling that is present on physical examination. The character and extent of the scaling are important in determining the specific type of ichthyosis. Age at onset of the condition, family history, and associated symptoms help determine the appropriate work-up of individual patients.
Onset of symptoms
Some of the hereditary ichthyoses present with symptoms at birth, while others may not present with clinical findings until infancy or childhood.[13] For example, with the autosomal recessive group of ichthyoses, a collodion membrane is often present at birth. X-linked ichthyosis and ichthyosis vulgaris are often not apparent at birth, but present in infancy sometime after 3 months of age.
For patients who develop scaly skin in adulthood, acquired ichthyosis should be considered. Because acquired ichthyosis can be due to medications or underlying disease, a detailed drug history, medical history, and review of systems are necessary.[14] Depending on the findings, further testing may be appropriate to help reveal the underlying cause of an acquired ichthyosis: CT scans may demonstrate a lymphoma; serum glucose levels may be elevated in cases of diabetes mellitus-associated acquired ichthyosis; and serological testing may provide evidence of autoimmune disease such as systemic lupus erythematosus.
Ichthyosis can cause a number of symptoms beyond the scaling itself, including pruritus, pain induced by skin fissuring, malodour caused by increased bacterial colonisation, ectropion, alopecia, and temperature dysregulation due to a decreased ability to sweat.
Family history
The presence or absence of ichthyosis in family members may help to determine the type of ichthyosis present in the patient. For instance, in patients with ichthyosis vulgaris, a dominantly inherited ichthyosis, there are often other family members who exhibit features similar to the patient's. However, because many patients possess de novo mutations in the dominantly inherited ichthyoses, the absence of affected family members does not rule out the dominantly inherited ichthyoses.[15]
Associated cutaneous findings
Ichthyosis vulgaris is commonly associated with other features present in atopic individuals such as keratosis pilaris and hyperlinear palms.[16] Autosomal recessive congenital ichthyosis can be associated with alopecia and ectropion.[17] Netherton's syndrome, an ichthyosis due to a defect in a serine protease inhibitor, commonly features trichorrhexis invaginata, a microscopic finding of a hair shaft that invaginates into a hair shaft below it.[18][Figure caption and citation for the preceding image starts]: Hyperlinear palmFrom the collection of Dr Timothy Patton; used with permission [Citation ends].
Involvement of other organ systems
Serious defects in other organ systems are typically present in the rarer ichthyoses, including Sjogren-Larsson (associated with spastic paraplegia), keratitis ichthyosis deafness (KID) syndrome (deafness, keratitis), Refsum's disease (deafness and ataxia), chondrodysplasia punctata (skeletal dysplasia), and others.[17] In X-linked ichthyosis, cryptorchidism and corneal opacities may be present.[19]
Biochemical tests
If X-linked ichthyosis is suspected, the diagnosis can be confirmed by demonstrating elevated levels of serum cholesterol sulfate and/or decreased levels of steroid sulfatase activity.[1][20] Lipoprotein electrophoresis showing an increased mobility of beta-lipoprotein is a convenient way to screen for steroid sulfatase deficiency, although it is not as sensitive as testing for elevated serum cholesterol sulfate. X-linked ichthyosis is typically not present at birth, but presents with fine peeling of the entire integument at the age of 1 to 3 weeks and demonstrates fine scaling in early life. Later, affected individuals typically develop polygonal dark scales. Flexures are also involved, but often to a minimal extent mimicking ichthyosis vulgaris.[1]
Serum phytanic acid is elevated in Refsum's disease; however, the test is not widely available and would not be commonly ordered in most patients who present with ichthyosis.
Genetic testing
Many of the underlying genetic defects of the ichthyoses have been determined and can be diagnosed with molecular testing.[5] If clinical suspicion is high, these tests may be considered first-line testing.
Skin biopsy
Skin biopsy is generally unhelpful in differentiating the various types of ichthyosis.[21] The exception to this is epidermolytic ichthyosis, which classically demonstrates epidermolytic hyperkeratosis on biopsy.
Trichorrhexis invaginata, a microscopic finding of a hair shaft that invaginates into a hair shaft below it, is a common finding in patients with Netherton's syndrome.
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