Quiz 28: What is your diagnosis?

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Diagnosis: Quiz 28

Quiz 28

Answer: Idiopathic guttate hypomelanosis

Criteria for diagnosis clinically: Hypopigmented macules, some of them scalloped, scattered in confetti-like fashion in photodistribution are characteristic of idiopathic guttate hypomelanosis.

Differential diagnosis clinically: There is none.

Criteria for diagnosis histopathologically: On the left side of the section, a marked decrease in the number of melanocytes at the dermoepidermal junction and in the amount of melanin contained in the epidermis, the diminution in number of melanocytes and quantity of melanin being made even more striking by contrast to those same considerations in the tan skin continuous with it on the right side of the section, are findings of idiopathic guttate hypomelanosis.

Differential diagnosis histopathologically: There is none.

Clinicopathologic correlation: The hypopigmentation resulted from a dramatic decrease in the quantity of melanin in the epidermis secondary to a decrease in the number of melanocytes there. The surface of the lesion is smooth because the stratum corneum is normal.

Options for therapy predicated on knowledge of histopathologic findings: No treatment is effective in restoring pigment to lesions of idiopathic guttate hypomelanosis.

1) Idiopathic guttate hypomelanosis seems to occur in skin that has been exposed for decades to the effects of ultraviolet radiation. In this particular instance, the patient was tanned prominently and, that being the case, the contrast is striking between the epidermis in the zone of idiopathic guttate hypomelanosis on the left half of this section of tissue and the tan skin continuous with it on the right.

2) As the appellation for it denotes, the cause of idiopathic guttate hypomelanosis is not known, even though exposure to sunlight for years seems to be a factor inducing of it.

3) The sites most affected by idiopathic guttate hypomelanosis are the dorsum of forearms and the anterior surface of the leg. Lesions tend to appear first in middle age and new ones continue to develop over time.

4) Specialized stains, in particular, immunoperoxidase for Melan-A.

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