Randy Jacobs, M.D. Patient Education

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Porokeratosis DSAP



DSAP is an unusual inherited skin condition causing dry patches on the arms and legs.  DSAP is a special type of inherited "sun spot", different from ordinary sunspots (called solar keratoses). The tendency to DSAP is inherited as an autosomal dominant, which means on average 50% of the children of an affected parent will also have the tendency. However a certain amount of accumulated sun exposure and perhaps other factors are needed to bring this tendency out.


Who gets DSAP?

DSAP was first recognized in Texas but it is not uncommon in the rest of the world. It appears on the sun-exposed skin of people of European descent, becomes more prominent in the summer and may improve in winter.  New lesions have been provoked by ultraviolet light in sun lamps.  The average age which patients first notice DSAP is about 40, and its frequency in affected families increases steadily with age. It has not been seen in childhood.


Clinical appearance of DSAP

The DSAP lesion begins as a 1-3 mm conical papule, brownish red or brown in color and usually around a hair follicle containing a keratotic plug. It expands and a sharp, slightly raised, keratotic ring, a fraction of a millimeter thick, develops and spreads out to a diameter of 10 mm or more. The skin within the ring is somewhat thinned and mildly reddened or slightly brown, but a pale ring may be seen just within the ridge. The ridge itself is sometimes a dark brown. The central thickening usually disappears, but it may persist with an attached scale, follicular plug or central dell.  Sweating is absent within the lesions. Sun exposure may cause them to itch. In sunny areas, lesions may be present in very large numbers and may change from a circular to a polycyclic outline. In less sunny climates patients have fewer lesions, which tend to remain circular. In a few cases, the center of the area becomes considerably inflamed and covered by thick scale, and may ulcerate and crust. DSAP affects areas exposed to sunlight, appearing mainly on the lower arms and legs and arising more frequently on the lower legs of women than men. The cheekbone areas and cheeks may be affected. It has not been seen on areas habitually covered by clothes, or on the scalp, palms or soles.  Development of true skin cancer in DSAP is possible but uncommon.


Treatment of DSAP

Unfortunately in our present state of knowledge there is no very satisfactory treatment for DSAP. Over the years we have tried cryotherapy, 5 fluoro-uracil cream, Tretinoin or Tazorac cream, alpha hydroxy acid cream, More recently Vitamin-A drugs in oral and ointment form have been tried, but nothing has proved very effective.  Most people settle for just having the larger lesions frozen lightly and returning as necessary for further treatments. Sun protection is important.  Restriction of sun exposure by wearing long sleeves, skirts or slacks and using sunscreens on the legs and arms will certainly reduce the development of new lesions