10: Immune System

SECTION 10 Immune System



Section Editor: Rhea V. Morgan, DVM, DACVIM (Small Animal), DACVO



Allergic Reactions

Extramedullary Plasmacytoma

Malignant Histiocytosis and Histiocytic Sarcoma

Multiple Myeloma

Systemic Lupus Erythematosus in Dogs: Systemic Aspects


Allergic Reactions


Rhea V. Morgan, DVM, DACVIM (Small Animal), DACVO



BASIC INFORMATION



Description


Allergic reactions occur when components of the immune system react to substances called antigens. Antigens are usually proteins. They may be introduced to the body through the skin, respiratory tract, or gut, or by injection. The systemic allergic reactions discussed here are anaphylaxis, urticaria, angioneurotic edema, and drug allergies. Allergic skin diseases, respiratory diseases, and adverse food reactions are discussed in other handouts.


Anaphylaxis is a severe, life-threatening hypersensitivity reaction. It is rare in both dogs and cats. Urticaria, or hives, are acute, focal swellings of the skin that are very itchy. Angioneurotic edema is sudden, soft swelling of tissues beneath the skin, especially the pinnae of the ears, lips, eyelids, and tissues of the face. Angioneurotic edema is not itchy or painful, but the skin overlying the swollen tissue may be red in color. Drug allergies are immune-mediated hypersensitivity reactions that are produced by antibodies formed by the immune system against some component of the drug.



Causes


Many different allergens can cause anaphylaxis, urticaria, and angioneurotic edema, including venoms from insects, drugs (usually injectable), vaccines, and blood or plasma transfusions. Urticaria and angioneurotic edema may occur after exposure to certain foods, and they can rarely arise with events that release histamine in the body, such as exposure to heat, cold, or pressure.


Drugs that can cause reactions include antibiotics and antibacterials (sulfonamides, penicillins, cephalosporins, tetracyclines), chemotherapeutic agents (asparaginase, doxorubicin), vaccines, and other medications (propylthiouracil, levamisole, aurothioglucose, methimazole, others). The drug dose, duration, formulation, and route of administration may all affect drug reactions. In some cases, genetics may influence the likelihood of a reaction; for example, the Doberman pinscher is more sensitive than other breeds to sulfonamide reactions.



imageClinical Signs


In the dog, the target organ of anaphylaxis is the liver, so vomiting, diarrhea, respiratory distress, collapse, shock, and death can occur. In the cat, the target organs are the respiratory and gastrointestinal tracts, so facial itchiness, salivation, difficulty breathing, vomiting, diarrhea, shock, and collapse may be seen. Anaphylaxis may occur the first time an allergen is encountered.


Hives are localized or generalized red swellings or wheals in the skin. Dramatic sudden, soft, nonpainful swellings of the ears, eyelids, and face are typical findings with angioneurotic edema. If the edema affects the voice box area, the animal may have trouble breathing.


Drug allergies usually arise after the animal has been exposed to the drug for 5 or more days. A wide variety of signs may develop, including skin rashes, ulcerations, and scabby lesions; fever; joint swelling; pain in the muscles; weakness or wobbliness; kidney disease; hemolytic anemia; and decreased platelets.



imageDiagnostic Tests


Diagnosis is based primarily on the clinical signs. It is often difficult to identify the offending allergen in cases of urticaria or angioneurotic edema. Administration of a drug immediately before the onset of anaphylaxis is very suspicious. Diagnosis of drug reactions is often made by eliminating other conditions that could cause similar clinical signs and by improvement of the signs after the drug is withdrawn. Although drug reactions can be confirmed by a return of signs when the drug is reintroduced, this is not usually recommended for fear of a severe reaction.



TREATMENT AND FOLLOW-UP




imageTreatment Options


Anaphylaxis and severe drug reactions require immediate emergency treatment in the hospital, with intravenous fluids, supplemental oxygen, and administration of injectable steroids, epinephrine (adrenalin), and other drugs for shock. Urticaria, angioneurotic edema, and mild drug reactions are treated with injectable and oral antihistamines and steroids. For all allergic reactions, it is also important to withdraw or remove the antigen, if it is known.



imageFollow-up Care


Animals with severe allergic reactions are usually hospitalized for close monitoring for at least 24 hours. Monitoring may include measurements of heart and respiratory rates, blood pressure, and blood oxygen levels. Laboratory tests may be repeated to assess the effect of the reaction on liver and kidney function, blood sugar, blood cell counts, and blood clotting functions.


Most mild reactions are treated on an outpatient basis, but the animal may be rechecked daily if the signs do not respond quickly to treatment. Notify your veterinarian if the signs worsen or do not show steady improvement over the first 24 hours of therapy.



Prognosis


Anaphylaxis is a potentially life-threatening reaction that can be fatal if therapy is not started quickly and aggressively. Prognosis for urticaria, angioneurotic edema, and drug reactions are good to excellent. To prevent recurrences, exposure to the antigen should be avoided in the future.



SPECIAL INSTRUCTIONS:



Extramedullary Plasmacytoma


Rhea V. Morgan, DVM, DACVIM (Small Animal), DACVO



BASIC INFORMATION



Description


Extramedullary plasmacytoma is a tumor created by the proliferation of plasma cells, a type of white blood cell derived from B-cell lymphocytes. Most often, a solitary tumor develops and can be located in various areas of the body. Some plasmacytomas behave in a benign fashion; others exhibit more malignant behavior.


Unlike multiple myeloma, extramedullary plasmacytoma is not a widespread invasion of multiple organs by malignant plasma cells. (See the handout on Multiple Myeloma.)



Causes


It is not known why plasmacytomas develop. They are relatively common tumors in dogs but are rare in cats. In dogs, three forms of the disease have been described: tumors of the skin and mouth, tumors of the gastrointestinal (GI) tract, and solitary osseous plasmacytomas (SOP) of bone. Cocker spaniels appear to be predisposed to plasmacytomas. In cats, skin tumors occur most frequently, but the mouth, abdomen, eye, and brain may also be affected.


Under normal circumstances, plasma cells produce immunoglobulins (antibodies). Malignant plasma cells can produce large immunoglobulin proteins called myeloma proteins or M proteins. These proteins do not function like normal antibodies; instead they cause a variety of problems in different organs. In the dog, tumors of the skin and mouth do not usually produce these proteins but GI tumors may. SOP may progress over time to multiple myeloma, and these M proteins are always produced in multiple myeloma. In the cat, some plasmacytomas of soft tissue and bone produce immunoglobulins.



imageClinical Signs


Plasmacytomas of the mouth and skin are often pink, hairless, round, and smooth or ulcerated masses. Skin tumors occur commonly on the head, ears, and feet. GI tumors may cause vomiting, diarrhea (with or without diarrhea), decreased appetite, and weight loss. SOP may cause bone pain or pathologic fractures (fractures caused by weakening of the bone rather than trauma).



imageDiagnostic Tests


Routine laboratory tests and x-rays are often recommended to investigate the clinical signs and to search for tumors elsewhere in the body. Fine-needle aspiration of the tumor may reveal plasma cells. Biopsy is often required to confirm the diagnosis. Extensive testing is then needed to rule out the presence of multiple myeloma.



TREATMENT AND FOLLOW-UP




imageTreatment Options


Surgical removal is the usual treatment for oral and skin tumors of the dog. In some cases, radiation therapy or cryotherapy (killing of the tumor by freezing) may be considered, especially if the tumor is located in an area that makes it hard to remove.


GI tumors are often treated by surgical removal. In some cases, surgery is followed by chemotherapy with prednisone and melphalan. Surgery and/or radiation therapy may be tried for SOPs initially, but chemotherapy is often required later in the course.


Antibiotics may be administered following surgery. Additional therapy may be needed if high levels of immunoglobulin are present in the blood. (See the handout on Multiple Myeloma.)

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Sep 11, 2016 | Posted by in SMALL ANIMAL | Comments Off on 10: Immune System

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