Rapid Clinical Updates: Gell and Coombs for the Hospitalist-Slides

Slides

Pdf Summary

This presentation reviews the Gell and Coombs classification of hypersensitivity reactions and how to recognize dermatologic emergencies in hospitalized patients.

Key points on hypersensitivity:
- <strong>Type I</strong>: IgE-mediated, immediate reactions after prior sensitization. Presents as <strong>urticaria</strong> or <strong>anaphylaxis/angioedema</strong> within seconds to minutes.
- <strong>Type II</strong>: Antibody-mediated against cell-surface antigens, causing reactions within minutes to hours. Classic examples include <strong>blood transfusion incompatibility</strong> and autoimmune blistering diseases such as <strong>pemphigus vulgaris</strong>.
- <strong>Type III</strong>: Immune-complex reactions, including <strong>serum sickness</strong> and <strong>leukocytoclastic vasculitis (LCV)</strong>, typically occurring hours to days after exposure.
- <strong>Type IV</strong>: T-cell mediated, delayed reactions occurring days to a week after exposure. Includes <strong>allergic contact dermatitis</strong>, <strong>morbilliform drug eruptions</strong>, <strong>fixed drug eruption</strong>, <strong>DRESS</strong>, and <strong>SJS/TEN</strong>.

The dermatology emergency section emphasizes a practical framework: <strong>“the epidermis is dying, the dermis is dying, the deeper tissues are dying, or the blood vessels are dying.”</strong>
- <strong>SJS/TEN</strong> are severe epidermal necrolysis syndromes, usually drug-induced in adults. Early clues include <strong>mucosal involvement</strong>, <strong>non-blanching targetoid lesions with dusky centers</strong>, and a <strong>positive Nikolsky sign</strong>. Common culprit drugs include <strong>TMP-SMX, anticonvulsants (especially lamotrigine, carbamazepine, phenytoin), oxicam NSAIDs, allopurinol, and nevirapine</strong>.
- <strong>Dermal emergencies</strong> include infections like <strong>mucormycosis</strong> and inflammatory disease such as <strong>pyoderma gangrenosum</strong>.
- <strong>Subcutaneous tissue necrosis</strong> is highlighted by <strong>necrotizing fasciitis</strong>, classically with <strong>pain out of proportion</strong> and rapid progression.
- <strong>Vascular skin disease</strong> includes <strong>small-vessel vasculitis</strong> presenting with <strong>palpable purpura</strong> and <strong>retiform purpura/vasculopathy</strong>, often from microthrombi or embolic disease.

Overall, the talk teaches hospitalists how to rapidly identify the morphology and timing of drug and skin reactions to determine urgency and guide management.

Keywords

hypersensitivity reactions

Gell and Coombs classification

urticaria

anaphylaxis

Stevens-Johnson syndrome

toxic epidermal necrolysis

mucosal involvement

necrotizing fasciitis

palpable purpura

drug eruptions