The earliest and most striking diagnostic features in IP occurs in the skin as progressive rashes. It has four stages which may overlap. The first stage is the erythematous (red) and vesicular (blister-like) stage which appears in infancy and is often present in the newborn. This consists of redness, blisters, and boils. It is the initial manifestation in 90% of patients.. It may last from a few weeks to a few months. The extremities and the scalp are most often affected, but the rash can be present on any body part. This rash may recur at times in the first few months of life, and rarely ever later. The rash may be confused with the skin rash seen in other infectious diseases including chicken pox, herpes, impetigo, or scabies. However, virus is never found in the blisters Each of these diseases is more common than IP and can be fatal in infants, so an infant may be treated for an infection before the diagnosis of IP is made. Knowledge of a family history of IP will aid in efficient diagnosis. As serious as it looks, the rash does not seem to be painful, although clothing may irritate the blisters. Secondary infection from common skin bacteria should be treated if it occurs.
The second phase, which may overlap with the first, are blisters which develop a raised verrucous (wart-like) surface. The lesions look like pustules. There can be thick crusts or scabs with healing and areas of increased pigmentation (darkened skin). It may be present at birth (implying that the vesicular stage took place in the womb), but it usually evolves after the first stage in 70% of patients. The extremities are involved almost exclusively. This stage typically lasts months, but rarely as long as a year.
The third phase is the hyperpigmented stage in which the skin is darkened in a swirled pattern often described as a “marble cake” appearance. In some patients, the adjacent areas ultimately thin and widen leaving streaky hypopigmentation. It may be present at birth in 5-10% of patients but usually appears between 6 and 12 months of life. This may or may not correspond to the areas that were involved in stages I and II. The heavy pigmentation tends to fade with age in most affected individuals.
The fourth stage is the atrophic (scarred) stage. These scars often are present before the hyperpigmentation has faded and are seen in adolescents and adults as pale, hairless patches or streaks. These are most easily seen when they are on the calf or in the scalp. Once most patients reach adulthood (late teen and beyond), the skin changes may have faded and may not be visible to the casual observer.