S8C10VA2-Vasculitides

Immunologic Models for Histologic Patterns

Immune complex diseases (antigen-antibody reactions)

1. Arthus reaction (classic):

a. localized

b. fixation of antigen (antigen in excess = soluble complex)

c. suitable time lag for antibody production

d. subsequent exposure to antigen

e. activation of complement

S8C10VA2-1: The sequence leading up to a classic Arthus reaction is summarized in a list.

Vasculitis

(damage of collagen)

1. edematous disruption of collagen bundles

2. fibrillation of collagen bundles in reticular dermis

3. proliferation of fibrocytes

4. fibrinoid necrosis

5. neutrophilic necrosis (leukocytoclasia)

S8C10VA2-2: In an Arthus reaction, neutrophilic infiltrates and vascular phenomena are interrelated.

Immune Complex Diseases

(continued)

1. Arthus reaction:

a. chemotaxis

b. necrosis (leukocytoclasia, fibrinoid, thrombosis, and hemorrhage)

S8C10VA2-3: In the skin, damage to connective tissue of the reticular dermis often is a more prominent feature than frank necrosis of the walls of neighboring vessels.

Histologic Correlates

1. neutrophils -complement

2. edema and fibrinoid - vascular permeability

3. necrosis (leukocytoclasia - complement cascade, and lysosomes)

4. thrombosis - common pathway (Hageman factor)

S8C10VA2-4: Some of the factors involved in the Arthus reaction are listed. Histologic alterations are correlated with components of immune reactions.

Patterns of Epidermal Responses

1. ischemia

a. infarction of epidermis (coagulated ghost cells, and paucity of inflammatory cells)

b. infarction of dermis (wedge-shaped area of necrosis, associated with thrombosis of vessels)

S8C10VA2-5: Often, the epidermis over a vasculitic lesion is remarkably uninvolved. In some examples, the epidermis may show ischemic changes with sheets of keratinocytes showing increased cytoplasmic acidophilia and pyknosis of nuclei. As a variation, the zone of ischemia may be saucer-shaped with the convexity directed toward the basement membrane. Occasionally, a leukocytoclastic vasculitis is associated with a pustule in the epidermis.

Identity of Neutrophilic Angiitides with some

Lymphocytic Angiitides

1. clinical anaphylactoid purpura

a. lymphocytic angiitis part of histlogic spectrum

2. arthus reaction and serum sickness

a. lymphocytic angiitis part of histologic spectrum

S8C10VA2-6: In some immune complex diseases, a lymphocytic vasculitis is a part of the spectrum (i.e., a stage in the temporal sequence of histologic reactions).

Erythema Multiforme

(areas of papillary dermal edema)

1. lymphocytic infiltrates (“lymphocytic vasculitis”)

2. subepidermal vesicles form by edematous disruption of the papillary dermis

3. basement membrane remains attached to roof of vesicle

4. eosinophils in dermal infiltrates are a variable feature

5. spongiotic and reticulated vesiculation

6. rarely, fibrinoid necrosis of vessels is a feature

7. edema might be cited as a feature of altered vascular permeability (i.e., vasculitis)

S8C10VA2-7: Erythema multiforme might be characterized as a lichenoid lymphocytic vasculitis. Some of the phenomena in the so-called dermal variant are in common with similar phenomena in some examples of vasculitis.

Problems at an Immunologic Level

(Vasculitis; impact of immunologic findings)

1. accumulated evidence inadequate as an aid in diagnosis

2. conflicting immunologic findings may:

a. express evolutionary patterns in a single specific process or,

b. define a heterogeneous group of processes

3. identify a specific triggering process, but ensuing sequence may be shared with other vasculitides (common pathways)

4. be related to an inability to identify the responsible antigen

5. be evidence of heterogeneity (are all vasculitides related to immune complexes?)

S8C10VA2-8: The nature of a vasculitis, as encountered in a clinical setting, often is uncertain. Some of the difficulties in the evaluation of the nature of a specific example of a “vasculitis” are listed.

Immunopathological Classification

(cutaneous angiitides)

1. evidence of circulating immune complexes

a. immune complex cryoglobulins

b. intermediate complexes

c. anticomplementary serum

d. hypocomplementemia

(J. J. Cream)

S8C10VA2-9: There are approaches to the study of a vasculitic disorder which are more sophisticated than the mere interpretation of the patterns on a histologic section. Some of the approaches to a study of a vasculitis are listed. Note: list continued on  next page in sequence (S8C12VA3).

 

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