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Reactive infectious mucocutaneous eruption

Reactive Infectious Mucocutaneous Eruption (RIME): Pathogenesis & clinical findings Bacterial or viral respiratory infection (most common infectious agent is Mycoplasma pneumoniae) ↑ Proliferation of polyclonal B cells (antibodies secreted by different B cell lines) & ↑ antibody production Antibodies cross-react (react to multiple antigens) with antigens in host tissue causing inflammation & tissue damage Systemic & local inflammatory response targets infectious agent RIME prodrome (early symptoms indicating a forthcoming illness) Fever Malaise Cough Dyspnea Inflammation & tissue damage activate inappropriate immune responses at distal sites Authors: Sonia Czyz Reviewers: Shahab Marzoughi Jessica Revington Michele Ramien* * MD at time of publication Normal Mucosa Complement system activates as part of the immune response & produces various complement proteins Epithelium Lamina propria Complement proteins C3a & C5a attract other immune cells to the site of infection & initiate ↑ inflammatory responses Complement protein C3b tags pathogens & infectious agents to help immune cells identify them ↑ Leukocyte infiltrate (accumulation) in tissue & ↑ vascular permeability of surrounding tissues Skin tissue experiences immune-mediated damage from immune cells & active complement proteins Cutaneous lesions (abnormal surface skin growths or skin changes) Mucositis in RIME Legend: Pathophysiology Mechanism Antibodies bind to antigens & form active immune complexes to attack infectious agents Immune complexes circulate in the body to target infectious agents. Antigen excess forms additional immune complexes Immunoglobulin G antibodies specific to the infectious agent cross- react with antigens on keratinocytes (keratin- producing skin cells) & mucosal cells in the epidermis (outermost skin layer) Additional immune complexes continue circulating in the absence of an infectious agent & subsequently deposit in skin tissue & mucous membranes Antibodies & immune complexes Leukocyte infiltrate Destructive inflammatory response induced at mucosal & skin sites with no target pathogen or infectious agent Complement activation Mucosal sites experience localized intense inflammation & ongoing immune-mediated damage from active complement proteins Severe mucositis (inflammation & ulceration of the mucous membranes) Acute hemorrhagic (excessively bleeding) crusts & erosions, ulcers, or vesiculobullous lesions (fluid-filled blisters) in multiple mucosal sites Published Nov 8, 2025 on www.thecalgaryguide.com Full-thickness epithelium necrosis (tissue death) Lamina propria Sign/Symptom/Lab Finding Complications Mucositis in RIME Reactive Infectious Mucocutaneous Eruption (RIME): Pathogenesis and clinical findings Normal Mucosa Epithelium Bacterial or viral respiratory infection; most common infection is Mycoplasma pneumoniae Systemic and local inflammatory response towards invading microbe Lamina propria Polyclonal B cell proliferation and antibody production Full-thickness epithelium necrosis Prodrome: cough, dyspnea, malaise, fever ~1 week prior to mucocutaneous eruption The antibodies cross-react with host tissue causing inflammation and tissue damage Lamina propria Authors: Sonia Czyz Reviewers: Shahab Marzoughi * MD at time of publication Inappropriate immune responses at distal sites Molecular mimicry Immune complex activation Complement activation I would remove all of this Immunoglobulin G antibodies specific for invading microbe cross- react with antigens on keratinocytes and mucosal cells in the epidermis Circulating immune complexes form in antigen excess C3a, C5a, and C3b produced Deposition in skin and mucous membrane ↑ Leukocyte infiltrate and vascular permeability Severe mucositis (inflammation and ulceration of the mucous membranes Destructive inflammatory response at mucosal and skin sites Antibodies & immune complexes Leukocyte infiltrate Complement activation Acute occurrence of hemorrhagic crusts and erosions, ulcers, or vesiculobullous lesions in 2 or more mucosal sites Localized inflammation and immune response activate complement system which damage mucosal tissues Immune response leads to painful, red nodules typically on the shins Triggering localized, intense inflammation and immune- mediated damage in these specific mucosal sites. Legend: Widespread systemic immune response Erythema nodosum Urticaria Immune response results in hives or itchy welts on the skin. Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Cutaneous lesions Published MONTH, DAY, YEAR on www.thecalgaryguide.com