Imaging Studies
Radiography in focal dermal hypoplasia (FDH) may reveal osteopathia striata. Osteopathia striata consists of longitudinal striations in the metaphyses of the bones. The lesions are usually bilateral and symmetric, mainly involving the long bones and the sacral bone. In contrast, the vertebrae and iliac bones are typically spared.
Osteopathia striata is an idiopathic finding, which radiographically is manifested by linear vertical opacities that originate at an articular surface and extend into the diaphysis, where they gradually narrow and disappear. The thickened striations of lamellar bone are parallel to the axis of the long bones. The shape, density, and cortex of the affected bones are normal.
Osteopathia striata is commonly present in focal dermal hypoplasia patients; however is not a specific diagnostic feature. When osteopathia striata occurs as an isolated finding, with no associations, it is known as Voorhoeve disease. This is an asymptomatic finding that is often an incidental radiologic finding.
The radiographic diagnosis of osteopathia striata is a useful clue in individuals who have minimal phenotypic disease. A careful clinical history taking and dermatologic examination may lead to the diagnosis of focal dermal hypoplasia.
Prenatal ultrasonographic findings are variable. Imaging studies may reveal findings that range from nonspecific fetal growth delay to specific organ and/or developmental anomalies; all findings are contingent on the degree to which an individual is affected.
Consideration should be given to imaging of the reproductive tract in affected individuals.
Other Tests
Parents and siblings of patients with new, apparently sporadic cases of focal dermal hypoplasia (FDH) should be closely examined for subtle skin findings or other abnormalities. Prenatal testing/karyotype analysis, sequence analysis, and deletion analysis are available. Deletion analysis can be completed using fluorescence in situ hybridization (FISH) or array-based genomic hybridization.
Bidirectional sequence analysis of all coding exons and their intron-exon boundaries of the PORCN gene is now commercially available. In addition, targeted array comparative genomic hybridization (CGH) analysis with exon-level resolution (ExonArrayDx) is performed concurrently to evaluate for a deletion or duplication of one or more exons of this gene. The Genetic Testing Registry is a resource through the National Institutes of Health that provides information on laboratories offering genetic testing.
Clinicians should routinely screen persons with focal dermal hypoplasia to rule out cognitive and emotional/behavioral difficulties and offer timely treatment. Future research should focus on identifying risk factors for psychoeducational problems in this population. According to a 2016 study examining emotional, behavioral, adaptive, and intellectual ability in 17 subjects aged 3-55 years with focal dermal hypoplasia attending the 2013 Annual Family Conference of the National Foundation for Ectodermal Dysplasias, there was wide variability, with three participants (18%) exhibiting overall cognitive ability in the borderline-to-impaired range. [28] These findings are consistent with previous reports suggesting intellectual impairment in 15% of persons with focal dermal hypoplasia.
Procedures
Biopsy of the skin may be performed.
Histologic Findings
Early lesions demonstrate small perivascular lipocytes. Lipocytes may sometimes be noted in the papillary dermis. The atrophic reticulated patches of skin reveal attenuation of dermal collagen fibers with partial-to-complete loss of dermal collagen. Note the image below.
Photomicrograph shows the histopathologic findings in a skin biopsy sample. The image depicts the characteristic absence of dermal collagen and the accompanying appearance of adipose tissue in the dermis.
In mild cases, adipocytes may be noted only around dermal blood vessels; in severe cases, they may replace all or part of the dermal connective tissue. A layered effect sometimes occurs, with attenuated collagenous connective tissue lying both above and beneath an adipose layer. If the accumulation of adipose tissue is pronounced, it may cause the apparent herniation of subcutaneous tissue through the thinned skin.
The papillomatous lesions typically consist of a fibrovascular stalk composed of loose connective tissue with dilated vessels and a variable perivascular admixture of inflammatory cells.
The lentigolike, pigmented-macule lesions indicate increased amounts of melanin deposition in the basal epidermal keratinocytes, with an underlying mild dermal infiltrate of lymphocytes with numerous dermal melanophages.
In ultrastructural studies of affected skin, fibroblasts are diminished in number, small, and ovoid, with poorly developed cytoplasm and dilated, rough endoplasmic reticulum. A conspicuous feature is a marked and irregular thickening of the nuclear fibrous lamina.
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Typical facial features are asymmetry of the face with mild hemiatrophy, low-set protruding ears, a narrow nasal bridge, a broad nasal tip with unilateral notch of the nasal alae, and a pointed chin. Also note the reticular hyperpigmentation of the skin, sparse hair, and raspberrylike papillomas on the lips.
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Photograph shows characteristic linear, erythematous, raised and depressed macules that follow the lines of Blaschko. Also note oligodactyly of the hand (entire rays are absent).
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Photomicrograph shows the histopathologic findings in a skin biopsy sample. The image depicts the characteristic absence of dermal collagen and the accompanying appearance of adipose tissue in the dermis.
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Characteristic lobster claw deformity.
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Syndactyly.
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Image shows oligodactyly of the feet. Also note the reticular erythematous hyperpigmentation on the limbs.
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Characteristic lesions that follow the lines of Blaschko.
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Hyperpigmentation that follows the lines of Blaschko on the upper extremity.
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Slightly raised and pigmented macules and soft tumors are noted on this extremity.
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Close-up view of reticulate, mildly atrophic, erythematous macules and soft, rounded nodules.
