Pathology of Reactive Perforating Collagenosis
Perforating disorders of the skin are rare and it is often difficult to discriminate these conditions.
Patterson proposed the following classification system:
(i) Perforation as an incidental histological finding;
(ii) Secondary perforation (Example: In granuloma annulare, pseudoxanthoma elasticum, and chondrodermatitis nodularis chronica helicis), and
(iii) Primary perforating dermatoses
Primary perforating dermatosis is a heterogeneous group of disorders characterized by transepidermal elimination of dermal components such as collagen, elastin, or fibrin.
There are 4 main subtypes based on both clinical and histologic factors:
1) Reactive perforating collagenosis (transepidermal elimination of collagen) ,
2) Elastosis perforans serpiginosa (transepidermal elimination of thickened elastic fibers),
3) Perforating folliculitis and
4) Kyrle disease (3 and 4 transepidermal elimination of keratin)
In 1989, Rapini et al coined the term acquired perforating dermatosis (APD) as a distinct entity.
This disease usually develops in adulthood.
Acquired perforating dermatosis has been reported to occur in association with various diseases, but is most commonly associated with dialysis-dependent chronic renal failure or diabetes mellitus.
It may also be associated with hypertension, hepatitis, hypothyroidism, and chronic obstructive pulmonary disease.
Clinical and histological features of the disease are not uniform, and may resemble any of the four classic perforating disorders: elastosis perforans serpiginosa, reactive perforating collagenosis, perforating folliculitis or Kyrle's disease.
Clinically, acquired perforating dermatosis presents as local or generalized 1 to 10 mm papules with a central keratotic crater.
Although lesions may present anywhere on the body, there is a slight predilection for the lower extremities.
The mean age of presentation is at the fourth to fifth decade of life, although any age may be affected with no gender predilection.
The duration of disease varies from a few weeks to 8 years.
Histopathologically, this entity is characterized by cup-shaped invagination of the epidermis plugged with necrotic inflammatory debris and transepidermal elimination of collagen bundles.
Masson trichrome staining shows transepidermal elimination of the collagen bundles.
The pathogenesis of reactive perforating collagenosis is still somewhat unclear, but it has been reported that trauma resulting from scratching may induce damage to the epidermis or dermal collagen.
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