Idiopathic guttate hypomelanosis (IGH), is a benign skin condition characterized by the presence of many round or oval hypopigmented patches varying in size from a few millimetres to 2 centimeters.
The most common sites of occurrence are the upper and lower extremities, but it may also be found quite frequently over the trunk or face. Fair-skinned individuals normally have a higher incidence.
The number of patches usually increases with time but individual lesions remain the same size, and cause no symptoms whatsoever except mild pruritus, in a few individuals.
The anterior aspect of the tibia is a prime spot for these lesions, possibly due to trauma and relatively poor vascular supply in this region.
Small white spots on arms (Idiopathic guttate hypomelanosis). Image Credit: Tee11 / Shutterstock
IGH occurs more commonly with increasing age, and is found in 87% of people over the age of 40 years.
Females have a higher incidence, though perhaps the diagnosis is more frequently made in young women due to their high level of consciousness about the cosmetic disfigurement caused by the lesions. On the other hand, it may also be because the lower extremities are more likely to be sun-exposed in this category. The patches are more prominently seen in dark-skinned individuals.
IGH may be caused by the following:
- Ultraviolet rays, especially cumulative exposure
- Age-related skin changes
- Genetic factors such as an observed familial association in some cases, and there is also some evidence of HLA linkage
- Autoimmune conditions
The basic pathophysiology is thought to be due to the inability of the keratinocytes to perform their normal phagocytotic processes and insert melanosomes into the cytoplasm, despite the presence of a normal number of melanocytes. Local factors are also a potent influence in this developmental process.
Diagnosis and treatment
In most patients the presence of IGH is diagnosed by visual examination and biopsies are normally unnecessary.
Dermoscopic examination of the lesions shows hypopigmented macules with normally pigmented flecks dispersed within them as well as extending outwards from their perimeter.
The macules may be of different shapes depending upon the duration of the lesion. The condition should be differentiated from other hypopigmented conditions such as vitiligo, lichen sclerosus, pityriasis versicolor and pityriasis alba.
Numerous modalities of treatment have been tried for this condition, including corticosteroid injections into the lesions, topical calcineurin inhibitors or retinoids, chemical peels or cryotherapy, dermabrasion and laser resurfacing of skin.
Non-ablative fractionated carbon dioxide laser seems to be among the most promising techniques to induce healing of the lesions with normal pigmentation post-treatment. The basis of most of these therapies is the removal of the abnormal melanocytes with ingrowth from the adjacent normal skin zones to restore normal skin coloration.
Prevention of further lesion development is equally important in the management of patients with IGH; there is evidence that sun exposure plays a variable but important role in the pathogenesis of the condition.
The patient should be advised to wear long-sleeved high-necked shirts or tunics with pants which cover the lower extremities, and especially to avoid sun exposure between 10 am and 4 pm when ultraviolet radiation is especially concentrated.
Broad-spectrum sunscreen application is also essential on a regular hourly or two-hourly basis, depending on the level of perspiration or activity. The sunscreen should have an SPF (sun protection factor) of 30 or more. Tanning beds should also be avoided.