The skin lesions of IP progress through 4 stages
Cutaneous manifestations of IP follow the lines of Blaschko and occur in a chronological sequence of 4 stages, which may temporarily overlap.4
The first stage (the vesicular stage) is comprised of papules, vesicles, or pustules on an erythematous base. These skin lesions are present at birth or develop in the first few weeks of life in 90% of patients, and typically resolve around 4 months.5
The second stage (the verrucous stage) consists of wart-like papules and plaques. These most commonly develop between 2 to 6 weeks and resolve by 6 months.
The third stage (the hyperpigmented stage) is marked by linear or whorled brown pigmentation. These lesions typically develop during the first 3 to 6 months of life and slowly disappear in adolescence.6
The final stage (the hypopigmented/atrophic stage) develops in adolescence and may be permanent. It often affects the lower extremities with areas of hypopigmentation, atrophy, and an absence of hair.
The diagnosis of IP is made based on the presence of typical cutaneous findings of any stage, most commonly the characteristic vesicular rash and the classic Blaschkoid hyperpigmentation on the trunk that often fades in adolescence.7 Typical features on cutaneous histology, such as eosinophilic spongiosis and dyskeratotic keratinocytes, can support the diagnosis.
Abnormalities of the teeth, eyes, hair, nails, CNS (eg, seizures, mental retardation, or microcephaly), palate, and nipple and breast have also been seen during infancy and are permanent. The mother of a child with IP may have a history of multiple miscarriages of male fetuses.6
Distinguish the rash of IP from other blistering diseases
The differential diagnosis of IP includes other cutaneous blistering diseases, such as herpes simplex virus (HSV) infection and epidermolysis bullosa (EB).8 HSV infection is the most common misdiagnosis in a neonate with vesicles, especially when seizures are also present.6 EB is a rare group of inherited disorders that manifest as blistering of the skin in infants, most commonly affecting the fingers, hands, elbows, feet, legs, and diaper area.
The distribution of skin lesions along the lines of Blaschko, the progression of the rash through different stages, and the possible maternal history of spontaneous abortions can distinguish IP from both HSV infection and EB.6 Cutaneous histopathology is also helpful for differentiating vesicular lesions in infancy and can confirm the diagnosis of IP.