Page 619 - Concise Pathology for Exam Preparation ( PDFDrive )

604 SECTION II Diseases of Organ Systems

Definitions of Microscopic Terms

• Hyperkeratosis: Thickening of stratum corneum, which may be associated with qualitative
abnormalities of keratin
• Parakeratosis: Retention of nuclei in the stratum corneum
• Hypergranulosis: Hyperplasia of stratum granulosum
• Acanthosis: Diffuse epidermal hyperplasia
• Papillomatosis: Surface elevation caused by hyperplasia and enlargement of contiguous
dermal papillae
• Dyskeratosis: Abnormal or premature keratinization within cells below stratum granu-
losum
• Spongiosis: Intercellular oedema of epidermis
• Acantholysis: Loss of intercellular junctions resulting in loss of cohesion between
keratinocytes
• Hydropic swelling: Intracellular oedema seen in keratinocytes
• Exocytosis: Infiltration of the epidermis by inflammatory or circulating blood cells
• Erosion: Discontinuity of the skin or incomplete loss of the epidermis
• Ulceration: Discontinuity of the skin or incomplete loss of the epidermis
• Lentiginous: Linear pattern of melanocyte proliferation within the epidermal basal
layer

Q. Define dermatitis.
Ans. Dermatitis is a nonspecific term, which indicates ‘inflammation of the skin’.

Q. Write briefly on eczematous dermatitis.
Ans. Eczema (spongiotic dermatitis) is characterized by a large group of pruritic skin
lesions with different aetiologies. Eczema has three stages: acute, subacute and
chronic.
1. Acute eczema is characterized by oozing, crusting and erythematous papulovesicular
eruptions with spongiosis (intercellular oedema) in the epidermis.
2. Subacute eczema is associated with crusts developing over ruptured vesicles in the
stratum corneum.
3. Chronic eczema shows raised scaly plaques or lichenification (thickening due to
hyperkeratosis from constant scratching) and hyperpigmentation.
Eczematous dermatitis is classified into the following:
1. Atopic dermatitis is a Type I IgE-mediated disease that presents in neonates as a rash
on the cheeks, trunk and extensor surfaces, and moves to the flexor creases as the child
grows older.
2. Allergic contact dermatitis is a Type IV cell-mediated hypersensitivity reaction against
poison ivy, oak, nickel and chemicals found in the household cleaners, cosmetics,
fabrics, dyes, medications and rubber products.
3. Irritant contact dermatitis, the most common type of eczematous dermatitis, is
a nonimmunologic reaction due to the local toxic effect of a chemical on the skin
(eg, detergents in soaps).
4. Photoeczematous dermatitis is a type of allergic contact dermatitis that is caused by
ultraviolet (UV) light reacting with drugs that have a photosensitizing effect (eg, tetra-
cycline, sulphonamides and thiazides).
5. Drug-related eczematous dermatitis: Reaction to an internal circulating antigen derived
from an ingested drug.
Morphology:
Spongiosis is defined as the accumulation of oedema fluid within the epidermis. Intercel-
lular bridges are stretched and become more prominent, giving rise to a spongy ap-
pearance. This is accompanied by superficial perivascular lymphocytic infiltrate and
papillary dermal oedema.
Note: There are no specific histopathological features to distinguish various causes of
eczema.

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