Dermatopathology.

A. Epidermal changes:

1. Hyperkeratosis is an increase in thickness of the horny layer. hyperkeratosis may be “absolute” –ie, an actual increase in thickness of the horny layer or “relative” in which it appears thicker in contrast to a thinner spinous layer.

2. Orthokeratosis is hyperkeratosis composed of cells that cornified completely and have no retained nuclei.

3. Parakeratosis is hyperkeratosis in which pycnotic nuclei in the squamous cells of the horny layer. Parakeratosis is usually seen in diseases where is an accelerated rare of epidermis cell turnover (psoriases). A diminished or absent granular layer is usually found beneath areas of parakeratosis. In condition such as chronic eczema, there may be areas of parakeratosis coexisting with serous exudates, causing a scale-crust over the surface of the epidermis.

4. Hypergranulosis is an increase in the number of keratinocytes in the granular later, often associated with orthokeratosis.

5. Hypogranulosis is a decrease in the number of keratinocytes in the granular layer.

6. Hyperplasia is an increase in the number of keratinocytes that results in thickened epidermis. Characteristically, there are 4 patterns of epidermal hyperplasia: psoriasiform (evenly elongated rete ridges), irregular (unevenly elongated rate ridges), papillated (digitate upward epidermal projections), and pseudocarcinomatous (extreme hyperplasia that may resemble a well-differentiated squamous cell carcinoma). The term acanthosis denotes thickening of the spinous or prickle cell layer.

7. Hypoplasia is a decrease in the number of keratinocytes that results in a thinned epidermis.

8. Hypertrophy is an increase in size of keratinocytes that leads to a thickening of the epidermis.

9. Atrophy is a decrease in size of keratinocytes, resulting in a thinned epidermis.

10. Spongiosis is intercellular edema between the keratinosytes, resulting in widening of the intercellular spaces and later leading to a spongy appearance or an intraepidermal vesicle. Spongiosis is an important histopathologic sign of eczema.

11. Ballooning is intracellularedema of keratinocytes leading to loss of stain affinity (pallor) and later cellular rupture with formation of multiloculated intraepidermal vesicles. This is an important finding in herpes virus skin infections.

12. Acantholysis is a loss of cohesion between individual keratinocytes that may lead to cleft, vesicle, or bulla formation. Acantholysis is an important sign in the pemphigus group of disorders.

13. Spongiform pustule is an accumulation of neutrophils between epidermal cells that may lead to a spongelike appearance and even vesicle formation. Spongiform postulation is a characteristic accompaniment of certain forms of psoriasis (pustular psoriasis).

14. Dyskeratotic cells are prematurely cornified keratinocytes that have eosinophilis cytoplasm and small dark-staining nuclei.

15. Necrosis is local death of cells. Necrosis can usually be identified because of the presence of nuclear fragmentation (karyorrhexis), nuclear ghosts (karyolysis), and nuclear shrinkage (pyknosis). In coagulative necrosis, all cellular detail may be lost apart from cellular outlines, but in caseation necrosis all cellular details are destroyed.

16. Vascuolar degeneration of thebaal cell layer is development of slitlike spaces above and below the basement membrane at the dermal-epidermal junction, which later leads to clefts and sometimes vesiculation.

B. Dermal changes:

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