Derm Dx: White spots on the legs - Clinical Advisor

Derm Dx: White spots on the legs

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  • IGH 1_1012 Derm Dx

  • IGH 2_1012 Derm Dx

  • IGH 3_1012 Derm Dx

A 52-year-old black female presents complaining of white spots on her legs. She is uncertain how long they have been present, but estimates between two and five years. Similar spots are present on her arms, albeit fewer in number.

The patient is otherwise healthy and takes no medications. Her family history is noncontributory. A total body skin exam is significant for small white spots on her legs and forearms.

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Idiopathic guttate hypomelanosis is a very common acquired disorder that occurs in individuals aged 40 years and older. Approximately 80% of people aged older than 70 years experience the skin condition. The eruption occurs in all skin types but is...

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Idiopathic guttate hypomelanosis is a very common acquired disorder that occurs in individuals aged 40 years and older. Approximately 80% of people aged older than 70 years experience the skin condition. The eruption occurs in all skin types but is more noticeable in darkly pigmented races. Females may be affected more than males.

Idiopathic guttate hypomelanosis lesions appear as small white macules located mainly on the shins and forearms. The face is not affected and the trunk is largely spared. The individual macules are smooth and irregularly shaped, have sharply defined borders, remain stable in size and do not coalesce. They appear as depigmented or hypopigmented freckles and do not spontaneously repigment.1,2

Although the etiology of the eruption is unknown, sun exposure may play a role. Lesions have occurred after UVB therapy. Histologically, there is flattening of the dermal-epidermal junction and a reduction or absence of melanin granules in the affected epidermis. There is also a reduction in the number of melanocytes, but the melanocytes are not completely absent as in vitiligo.1,2

Diagnosis

Idiopathic guttate hypomelanosis diagnosis is based on the clinical appearance of small whitish macules exclusively on the extremities of an older individual. When the diagnosis is in doubt, a skin biopsy may be considered, but this is rarely indicated.1,2 

Progressive macular hypomelanosis is a common disorder, mainly affecting darkly pigmented young women. Asymptomatic hypopigmented macules and patches on the trunk are characteristics of the condition. These hypopigmented areas are poorly delineated and non-scaly. Rarely hypopigmentation may extend to the proximal extremities or neck. The etiology is unknown but the bacteria Propionibacterium acnes have been implicated. 1

Pityriasis lichenoides chronica defines a chronic acquired eruption in which erythematous macules and papules slowly progress to hypopigmented macules and patches. The eruption may resolve spontaneously over weeks to months, but it some cases it persists for years.3

Tuberous sclerosis is an autosomal dominant congenital disorder due to mutations in harmartin and tuberin. Ash leaf macules and confetti macules are the earliest finding and appear as polygonal or confetti shaped hypopigmented macules. They are usually congenital. This contrasts with idiopathic guttate hypomelanosis in which the lesions are acquired in late adulthood and are restricted to sun exposed areas. 

Other manifestations of tuberous sclerosis include connective tissue nevi, angiofibromas, café au lait macules, retinal hamartomas, renal angiomyolipomas and cysts, cardiac rhabdomyomas, pulmonary lymphangiomyomatosis, dental enamel pits, oral fibromas, mental retardation, cortical tumors and subependymal nodules. 

Treatment

There is no standard treatment for idiopathic guttate hypomelanosis. Liquid nitrogen has been cited as a potential therapy; however, this treatment is known to cause leukoderma, especially in darkly pigmented individuals. therefore, one must proceed cautiously if this therapy is attempted. 1,2

Adam Rees, MD, is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine in Houston.

References

1. Bolognia J, Jorizzo JL, Rapini RP. “Chapter 65: Vitiligo and Other Disorders of Hypopigmentation.” Dermatology. St. Louis, Mo.: Mosby/Elsevier, 2008.

2. James WD, Berger TG, Elston DM et al. “Chapter 36: Disturbances of Pigmentation.” Andrews’ Diseases of the Skin: Clinical Dermatology. Philadelphia: Saunders Elsevier, 2006.

3. James WD, Berger TG, Elston DM et al. “Chapter 32: Cutaneous Lymphoid Hyperplasia, Cutaneous T-cell Lymphoma, Other Malignant Lymphomas, and Allied Diseases.” Andrews’ Diseases of the Skin: Clinical Dermatology. Philadelphia: Saunders Elsevier, 2006.

4. Bolognia J, Jorizzo JL, Rapini RP. “Chapter 10: Other Papulosquamous Disorders.” Dermatology. St. Louis, Mo.: Mosby/Elsevier, 2008.

5. James WD, Berger TG, Elston DM et al. “Chapter 27: Genodermatoses and Congenital Anomalies.” Andrews’ Diseases of the Skin: Clinical Dermatology. Philadelphia: Saunders Elsevier, 2006.

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