Exam 6 Flashcards
Clinical Signs and Diagnostic Testing for Immune Mediated Disease
Discuss basic tenets and components of innate vs. acquired immune systems
Natural/Innate
-Phagocytic WBCs
-Prior exposure to antigens not required
-Complement proteins
-Natural killer lymphocytes
Acquired
-Prior exposure to antigen required
Antigen
-Any substance capable of inducing an immune response
-Immune response = production of antibodies
-Cell mediated response via T-Lymphocytes
Antibody
-Protein molecule produced by B-lymphocytes/plasma cells in response to specific antigens (aka immunoglobulins)
Acquired immunity
-T and B lymphocytes responses:
-IgG, most prevalent, any time exposure, passive immunity mostly. Monomer, phagocytosis
-IgM, means recent exposure, Pentomer (largest antibodies), viruses.
-IgA, Prevalent in secretions (saliva, milk, sweat), Mucosal surfaces.
-IgD, Mature B-lymphocytes, induction of tolerance during fetal development
-IgE, VIP for allergic reaction, degranulation = eosinophils recruitment
T-Lymphocytes = Helper = CD4+ MCH2 receptors = Cytokines, inflammatory cascade
B-Lymphocytes = Cytotoxic = CD8+ MCH1 receptors = antigen mediated attack and destruction
Regulatory T-Lymphocytes = regulate inflammatory response.
T-Cells
Th0: naive
Th1: Cell-mediated immunity and inflammation
Th2: Antibody-mediated
T-reg: Immune tolerance
Superantigens
-Staphylococcus aureus
-Streptococcus pyogenes
-Mycoplasma arthritiditis
-Pseudomonas aeruginosa
-Clostridium perfringes
The complement system pathways
- Classic pathway
-C1-C4 proteins
-Primarily activated by IgG and IgM
- Alternative pathway
-C3, B, D, and P proteins
-Key player in innate immunity
-Can be activated by microbial surface proteins in the absence of antibodies
- Terminal pathway
-After one of the previous pathways has been activated
-Results in the formation of the membrane attack complex
-Water and ions diffuse through holes created in the cell membrane leading to rupture
Discuss clinical signs and symptoms seen in C/F patients with common immune mediated diseases
Discuss pathogenesis and review of the four major hypersensitivity reactions (type I-IV)
Type I
-Allergic, Anaphylaxis, Atopy
-IgE mediated
-Histamine and bradykinin
-Activates the complement and coagulation systems
-Hives, atopy, lymphoplasmacytic enteritis, eosinophilic granuloma complex.
Type II
-AntiBody
-IgG or IgM mediated
-Soluble complexes formed
-Ex: penicillin, sulfas, Anaplasma, Babesia, IMHA, ITP, pemphigus, myasthenia gravis.
Type III
-Immune Complexes
-IgG mediated
-Excessive amount of antigen compared to antibodies
-Deposits in kidneys, joints
-Damage to host tissue via classic pathway
-Ex: glomerulonephritis, lupus, vasculitis
Type IV
-Delayed
-Takes 24 hours to develop, weeks for maximal response, and months to resolve completely
-T-lymphocytes
-Mononuclear inflammation
-Ex: cutaneous drug reaction
Discuss the diagnostic testing approach to the patient with common immune mediated diseases for each diagnostic modality
The key phenomenon behind any immune mediated disease is the loss of self-tolerance
-May be generalized or organ specific
-Multifactorial influences
C/S
-Non specific
-Ddx infectious or neoplastic
- Minimum Data Base
- Great history and PE
- CBC, chem, UA
- Play the hunt: chest rads, abdominal rads, ultrasound.
Treatment of Immune mediated diseases
Key = halt the immune reaction underlying the disorder without turning off the immune system completely, increasing the risk for a serious infection
Discuss principles of treatment for immune-mediated diseases in the C/F patient
- Halt immune reaction
- Not fully turning off immune system
- Lowest dose necessary to control disease
- Least number of medications necessary
- Most specific therapy best
Discuss the side effects of immunosuppressive therapy
-Infection
-Vomiting, diarrhea, anorexia
-Bone marrow suppression
-Hepatotoxicity
-PU/PD/PP. panting, muscle wasting, hepatomegaly
-Insulin resistance/antagonism
Discuss how to monitor a patient receiving therapy for immune-mediated disease and appropriate supportive care for the patient when side effects arise
-Routine examinations
-Recheck labs: CBC/Chem?UA/urine culture. 2 weeks post initiation then q3-6 mts or as indicated
-Therapeutic drug level blood testing when available
-Supportive care: ex: liver antioxidants
Discuss glucocorticoid physiologic, anti-inflammatory and immunosuppressive therapy dosing strategies, including differing potencies of individual glucocorticoids and side effect of glucocorticoids
MOA
-Stabilizes the cell membrane
-Inhibition of chemotactic factors production, altering leukotrienes inflammatory mediators
-Inhibit Phospholipase A2
-Inhibiting the release of arachidonic acid, decreasing the production of prostaglandins and leukotrienes
-Blocks NF-kB
-Modifies protein, carbohydrate and fat metabolism
-Suppress acute inflammation by inhibiting vascular permeability, vasodilation, and leukocyte migration from capillaries
Side effects
-PU/PD
-Weight gain (muscle loss with redistribution of fat)
-Calciuresis - calcium oxalate calculi
-Insulin resistance - diabetes mellitus
-Fluid retention, volume overload, CHF
-Thromboembolic disease, hypercoagulability
-Infectious
-Vomiting, diarrhea, etc.
Discuss other pharmacologic immunosuppressive therapies and non pharmacologic immunosuppressive adjunctive therapies used to treat common immune mediated diseases in the C/F patient
Cyclosporine
-Blocks calcineurin-mediated T-cell activation
-Inhibits production of IL-2, IL-3, IL-4, TNF-alpha, INF-gamma
NOT myelotoxic, effect is not noted immediately
-Cytochrome P450 system metabolism in liver
-Caution in patients with MDR1 mutation (Collies, Australian Shepherds)
Dosage reductions to remember
-Ketoconazole: up to 75% reduction in Cyclosporine dose
-Fluconazole: up to 30-50% reduction
Immunosuppressive dose: 3-6mg/kg PO BID
-Vomiting, diarrhea, anorexia, promotes development of neoplasia especially lymphoma in dogs/cats
-Peak: 2 hours after administration
-Trough: 12 hours canine (500ng/ml), feline (300-600 ng/ml)
-Cytokine levels can be re-checked 7-10 days after dose adjustment
Azathioprine
MOA
-Acts as a purine analog
-Metabolized to ribonucleotide monophosphate
-Leads to intracellular accumulation of monophosphates = feedback inhibition of further nucleotide synthesis
-Decrease antibody formation
-Suppresses macrophage function
Clinical response up to 6 weeks
Cats highly susceptible to myelosuppression due to low thiopurine methyltransferace NOT recommended for cats
-Giant Schnauzers also similar to cats
-Light sensitive drug
-Interactions: Ace inhibitors, Allopurinol, Corticosteroids
Azathiaprine
-Myelosuppression: non regenerative anemias long term
-Pancreatitis
-Mutagenic/Teratogenic
DO NOT split tablets
-Caution: pregnant females avoid handling drug.
2mg/kg PO SIB, then reduce after 1 week
-Recheck CBCs/Chem every two weeks
Mycophenolate Mofetil
MOA
-Inhibts inosine monophasphate dehydrogenase
-Rate limiting step for purine synthesis
-Inhibits T and B lymphocytes proliferation
-Suppression of antibody formation and leukocyte recruitment
Non myelotoxic replacement of Azathioprine
-Give on an empty stomach preferably
GI, and Enterocolitis side effect
Drug interactions
-Antacids, aspirin, azathioprine, iron
8-12 mg/kg PO BID dog, 10mg/kg PO BID feline
-Recheck CBCs every 2-3 weeks, then 2-3 months
Leflunomide
MAO
-A synthetic organic isoxazole
-Prevents pyrimidine synthesis
-Decrease DNA and RNA synthesis, at higher concentrations inhibits tyrosine kinases
-Metabolized by intestinal mucosa
-Time to peak: 5 hours dogs, cats 8 hours
-Highly protein bound
-Less drug interactions
Canine 2mg/kg PO SID, feline 2-3 mg/kg
-Elevated liver enzymes in dogs
-Monitor CBC and liver chemistries, 2 weeks then 1-2 months
Cyclophosphamide
MOA
-Acrolein
-4-OHCP
-Suppresses both T cell and antibody production
-Alkylation of DNA
-Peak concentration 45 minutes PO or IV
-Minimal protein binding
Cyclophosphamide-induced Cystitis CIC in dogs
-Hemorrhagic cystitis
-Pulmonary infiltrates
-Myelosuppression WBCs
Drug interactions
-Allopurinol
-Cyclosporine
-Chloramphenicol, etc.
Dog: Do NOT exceed 4 weeks, 150-200mg/m2 weekly divided in three days
Feline 2-2.5 mg/kg PO SID
-Recheck once per week, no refills.
AVOID in patients with IMHA
Adjunct therapies
Intravenous Immunoglobulin
MOA - hypothesis
-Neutralizes antibodies
-Negative feedback
-Suppressing cytokines and phagocyte activity
-No drug interactions
-Rapid onset of action
-Elimination half-life 7-9 days
Side effects
-Hypertension
-Anaphylaxis risk
-Volume overload, colloid like properties
-Thrombotic events
Salvage procedure
Other Treatment
-Splenectomy
-Plasmapheresis
Common Immune Mediated Diseases
Discuss the etiology, clinical features, diagnosis, treatment, complications, and prognosis
Canine IMHA (primary vs secondary)
Pathogenesis
-Autoantibodies bind to antigen on the erythrocyte membrane
-Complement or antibody mediated RBC destruction
-Removed from circulation
Intravascular
-Free Hemoglobin within the plasma and urine
-Mores sick
-More transfusions
Extravascular - more common
-More gradual
-Bilirubin in urine and plasma
-Spleen and liver antibody, reticuloendothelial system
Primary
-Idiopathic or autoimmune
-Most common
-Hemolysis in the absence of trigger
Secondary
-Neoplasia
-Infectious disease
-Drug interactions: may resolve quicker
Triggers will dictate the diagnostic workup
Other types of hemolytic anemia
Non-immunologic Hemolytic Anemias
- Fragmentation
-DIC
-Caudal caval
-Torsion (spleen, liver, GDV)
-Valvular disease
-Neoplasia
-Vasculatis
-Schistocytosis
- Toxicant Induced
-Onion, garlic, PG, Acetaminophen, Benzocaine, Zinc, Copper, Naphthalene, Antibiotics.
-Haptens secondary response
- Heritable
-Phosphofructokinase deficiency: Crocker Spaniels
-Pyruvate kinase deficiency: RBC breakdown: Basenji, Beagle, Cairn, Lab, Pug, WHWT
-Osmotic fragility
- Metabolic
-Hypophosphatemia
-Hemolytic-uremic syndrome
-Osmolarity changes (HHS)
-Envenomation
-Hypotonic fluids
Common Clinical Signs
-Middle aged to older dogs
-Females
-Crocker Spaniel, Shih Tsu/Lhasas, Duchshunds, Labradors, Poodles, Border collies, Springer spaniels.
-Warmer months
-Lethargy, weakness, anorexia, vomiting, pigmenturia, brown or bloody urine, icterus, collapse
-Tachycardia
-Tachypena
-Systolic ejection murmur
-Hepatomegaly
-Fever
Diagnosis
-3 causes of anemia
-Look for sequelae
-Determine primary or secondary
- Loss
-Decreased albumin, globulin, TP
-Secret GI bleeding!!
-Evidence of external or internal hemorrhage - Decreased production
-Usually normal TP
-Without evidence of hemolysis (bilirubin, hemoglo binemia)
-Pancytopenia
-No evidence of regeneration (polychromasia, reticulocytes)
-Reticulocytes 3-5 days to regenerate - Hemolysis
Tests
-CBC
-Chemistry
-Urinalysis
-PCV/TS: severe if <25%
-Blood smear: Heinz bodies = precipitated hemoglobin, denatured RBCs, indicative of oxidative injury, toxins garlic, onion.
-Spherocytes: the slam dunk cell! loss of central parlor, Antibodies bound leads to cytophagocytosis
-Slide agglutination
-Hemoglobinuria/hemoglobinemia
-Leukocytosis: can be very high
-Bilirubinuria/bilirubinemia
-Prognostic >60,000
-Thrombocytopenia
-Platelet <30,000
-Concurrent tick borne disease possible
Coombs Test
-Definitive for IMHA
-AKA direct antiglobulin test
Heptan Molecules
-Recent vaccination
-Within 3 weeks
-Sulfas, penicillins, cephalosporins
Treatment
-Improve DO2: IV fluids, transfusions, no pre-med, 1-4 hours transfusion, watch for fluid overload
-Treat underlying cause/trigger
-Immune suppression
-Manage hyper coagulable state
Transfusion trigger
-Tachycardia
-Syncope
-Hyperlactemia
-Chronicity
-Comorbidities: fluid overload due to anemia
Meds
-Steroids: mainstay of treatment
Prednisone best
-Decrease IFN, IL2, suppress T cell function
2mg/kg/day Max 60 mg per day
Rescue Meds
-Mycophenolate Mofetil: 10mg/kg BID. GI effects. Inhibitor of purine synthesis
-Azathioprine: Thiopurine analog. Works in 10-14 days, cheaper than cyclosporine . 2mg/kg/day, big dogs 40-50mg/m2. SID x 7d. Pancreatitis
-Cyclosporine: Blockage of calcineurin, IL2, IL3, IL4, TNF. 5mg/kg BID
-hIVIg: FC receptor blockage, rapid onset
-Splenectomy: risks anesthesia, thrombosis, bleeding.
Thromboembolic events
-Hypercoagulable state
IMHA hyper coagulable state
-Expression of tissue factor on monocytes and endothelium
-Binding of F VII initiation of coagulation
-Phagocytosis of RBCs trigger CKs and TF expression, free hemoglobin decreased NO = platelet aggregation and vasoconstriction
-Thrombi in 46-80% of non-survivors
-DIC in 45%
-Early anticoagulant treatment is warranted
-Venous thrombi: fibrin rich, low shear stress
-Arterial thrombi: high shear stress, platelet activation.
Test Dx
-PT/PTT
-ACT
-Specific factor antigen assay
-AT, fibrinogen
-FDPs and D dimers
-thromboelastography (fancy test)
Tx
-Clopidrogel: ADP, PAR1 binding, decrease activation of fibrinogen R
-Aspirin: TXA2 decreased
-Heparins: PTT check, risk of bleeding (LMWH)
-Thrombin inhibitors: Ximelgatan & Dabigatran
-Anti-Xa drugs: Rivaroxaban, Apixaban
CHAOS score
PRCA, PIMA, IMHA
PIMA
-Precursor directed immune mediated anemia
-PCV <10%
-Erythroid hyperplasia, bone marrow analysis
-Tx: transfusion, splenectomy
-Thromboembolic 50%
Feline IMHA
-2nd more common than primary
Never Azathioprine to cats
Causes
-FeLV, FIV, FIP, Babesia felis, Mycoplasma haemofelis, cytauxzoon
-Neoplasia
-Drugs: methimazole, penicillin, TMS, levamisole
-Inflammatory diseases and other causes: SLE, cystitis, prostatitis, pyothorax.
-Similar treatment and monitoring
Thrombocytopenia
-Spurious is common
Make a smear, don’t always trust the machine
-Decreased production in bone marrow, infectious = consumptions, sequestration spleen/liver due to SLE, ehrlichiosis
ITP - Immune Mediated Thrombocytopenia
-Anti-platelet antibodies
-Crocker spaniel, mini poodles, OES, Vizlas, Scotties, Dachshunds
2nd ITP causes
-Drugs: sulfas, cephalosporins, vaccines, neoplasia, HSA, myeloma, RMSF, Ehrlichia, ana plasma
-Spontaneous bleeding if <40-50k count
Dx
-Confirm platelet count
-CBC, chem, UA
-Infectious dz PCR/serology
+/- Neoplasia hunt, platelet antibody testing, bone marrow aspiration/biopsy
Treatment
-As per IHMA
-IV IgG can be considered when severe hemorrhage
Doxycycline 4 weeks when infectious negative still do it
SLE
-Type III hypersensitivity reaction
-Immune complex deposition with secondary neutrophilic inflammation
-Middle age
-GSD
-Large breeds
-No sex predilection
SLE Dx
-Positive ANA in 95% of cases, sensitive but not specific
-Plus 2-3 classical clinical symptoms
-Coombs’s positive in 17%
-Anti IgG ab 20%
Circulating immune complexes in 75% of cases
Treatment
-Prednisone
-Other immunosuppressants
-Prognosis: varies, poor if renal failure
Acquired myasthenia gravis
C/S
-Weakness and collapsing episodes
-Unable to get up on their own
-Lethargy
Ddx
-Lethargy: CV disease (syncope, arrhythmia), metabolic dz (hypoglycemia, hypokalemia), orthopedic (cruciate rupture, osteoarthritis), neurologic, neuromuscular (myasthenia gravis)
Dx
-CBC, chem, UA
-Ortophedic exam
-Neurological exam
Results
-Isosthenuria 1.012
-Orthopedic exam: no cranial drawer sign, no crepitus, good muscle mass, normal musculoskeletal exam
-Neuro: normal mentation, cranial nerves normal except: mild decreased gag reflex, palpebral decrease with repetitive stimulation. Conscious normal proprioception and sensation. Flexor reflexes decreased in all four limbs
Plan
-Radiographs thoracic
-Tensilon test
-Acetylcholine antibody titer
Results
-Megaesophagus with mild aspiration pneumonia
Therapeutic plan
-Acetylcholinesterase inhibition: Pyridostigmine
-Immunosuppression: Prednisone, mycophenolate
-Megaesophagus: elevated feeding
Review polyarthritis, MMM, dermatomyositis, perianal fistulas, glomerulonephritis
Congenital Macrothrombocytopenia
-Cavalier King Charles Spaniel
-Greyhound, Shiba, Polish Ogar. Ashi Cairns (cats)
-Affected dogs do not have bleeding disorders
Persistently low platelet count in absence of history or evidence of abnormal bleeding and is non-responsive to treatment with antibiotics or steroids