PITYRIASIS RUBRA PILARIS
Pityriasis
rubra pilaris (PRP) is an idiopathic rash that has many cutaneous
manifestations. It is an uncommon entity that often manifests with nearerythroderma.
There are several clinical variations of the condition, and it has a
characteristic histological pattern, although this pattern is not always seen
on microscopic examination.
Clinical Findings: PRP has a unique bimodal age of distribution, with an early onset of
disease in the first 5 years of life and adult onset in the sixth decade. There
is no gender or racial predilection. PRP tends to run a chronic course. It
starts insidiously with small follicular, keratotic, pink to red papules. These
papules have been described as “nutmeg grater” papules. The papules coalesce
into larger patches and plaques. Eventually, large surface areas are involved,
with a near-erythro-derma. Characteristic islands of sparing occur within the
erythrodermic background. These islands of completely normal skin are usually
small, a few centimeters in diameter, but they can be much larger. The islands
typically have an angulated shape, and they are rarely perfectly round or oval.
The palms and soles become thickened and yellowish. This is highly characteristic
of PRP and is called “carnauba wax–like” palms and soles. Fissuring is very
common within the keratoderma and can be a source of pain and a site for
secondary infection.
PRP has historically been separated into five
subtypes: classic adult, classic juvenile, atypical adult, atypical juvenile,
and a circumscribed or localized form. The classic adult and classic juvenile
forms were described earlier. They typically run a chronic clinical course,
with most cases spontaneously resolving a few years after onset. Paraneoplastic
variants of PRP have been described. Onset of the malignancy precedes the rash
of PRP, and the patients seem to improve with treatment of the underlying
tumor. This is a very rare clinical scenario. Patients with human
immunodeficiency virus infection seem to be at a higher risk for developing
PRP.
The differential diagnosis of classic forms of PRP
includes psoriasis, drug rash, and cutaneous T-cell lymphoma. Skin biopsy and
clinical pathological correlation help the clinician make a firm diagnosis.
Pathogenesis: The etiology
is undetermined. Theories on the formation of PRP have centered on abnormal
metabolism of vitamin A or an abnormal immune response to a foreign antigen.
These theories have not been thoroughly studied or proven. The report of a familial form of PRP may
shed some light on the
etiology.
Histology: The
pathognomonic histological finding in PRP is the appearance of alternating
layers of parakeratosis and orthokeratosis, both in a vertical and a horizontal
direction, lending the appearance of a chess board. This pattern is not always
present, and sometimes it can be seen only with close inspection.
Treatment: Therapy for
PRP is difficult. Many agents have been used with varying degrees of success. Topical corticosteroid wet wraps, oral retinoids, and
ultraviolet therapy have long been used as first-line agents. The retinoids are
considered first-line therapy, and both isotretinoin and acitretin have been
used. Other immunosuppressants have been used, including methotrexate, azathioprine,
and the newer anti tumor necrosis
factor inhibitors. No randomized, placebocontrolled trials have been performed
to date.
