Hypersensitivity disorders Flashcards
Rash in response to irritants/food/environment most present in first year of life
A. Atopic dermatitis (eczema) - type 1 hypersensitivity
Predisoposition to S. auerus superinfection
Mx - emmolient, topical steroids
Facial swelling, weals, and wheeze in after eating at a seafood restaurant
A. Shellfish (food) allergy - type 1 hypersensitivity
Others: milk, egg, nut
Ix - skin prick, food diary, RAST challenge
Mx - avoidance, Epipen
Allergy due to cross-reactivity of antigen, symptoms limited to mouth (anaphylaxis in 2%)
A. Oral allergy syndrome -type 1 hypersensitivity
Ix - skin prick
Mx - avoidance, wash mouth + antihistamine
Allergy to latex confers allergy to certain foods
A. Latex food syndrome - type 1 hypersensitivity
Nasal itch, coryza, sneezing in response to pollen/dust mites/ animals
A. Allergic rhinitis - type 1 hypersensitivity
Ix - skin prick and RAST
Mx - avoidance, steroid nasal spray, antihistamine etc.
Idiopathic or triggered IgE mediated wheals which resolve in six weeks
A. Acute urticaria - type 1 hypersensitivity
Eight steps in acute management of anaphylaxis
- Elevate legs
- 100% oxygen
- IM adrenaline 500mcg
- Inhaled bronchodilators
- IV Hydrocortisone 100mg
- IV Chlorphenamine 10mg
- IV fluids
- Call for help
What is a positive result in skin prick testing?
A. Wheal >2mm larger than negative control
What is the mechanism behind type 2 hypersensitivity?
A. IgG or IgM reacts with cell/matrix self antigen.
Causes neonatal jaundice (<24h) due to rhesus incompatibility
A. Haemolytic disease of the newborn - type 2 hypersensitivity
Ix - DAT +ve
Mx - Transfusion
Destruction of RBCs by autoantibody, complement and FcR+ phagocytes
A. Autoimmune Haemolytic Anaemia - type 2 hypersensitivity
Ix - DAT+
Mx - Steroids
Bruising and bleeding due to reaction with GpIIb/IIIa on platelets
A. Autoimmune Thrombocytopaenic Purpura - type 2 hypersensitivity
Ix - Antiplatelet ab
Mx - Steroids, IVIG, anti-D antibody, splenectomy
Glomerulonephritis + pulmonary haemorrhage
A. Goodpasture’s syndrome - type 2 hypersensitivity
Ix - Anti GBM ab (linear smooth if staning of IgG on basement membrane)
Mx - steroids and immunosuppresion
Non-tense blistering of skin and bullae. Nikolsky’s sign is positive (rubbing of skin results in separation of the outermost layer)
A. Pemphigus vulgaris - type 2 hypersensitivity to epidermal cadherins (demoglein 1 and demoglein 3)
Ix - immunofluoresence showing IgG deposition
Mx - steroids and immunosuppression
Anti-TSH-R Ab
A. Graves disease - type 2 hypersensitivity
Mx - carbimazole and propylthiouracil
Fatiguable muscle weakness and double vision, with abnormal EMG tensilon test
A. Myasthenia gravis - type 2 hypersensitivity
Ix - Anti ACh-R Ab
Mx - neostigmine, pyridostigmine, IVIG and plasmaphoresis (severe)
Presents with one or more of carditis, arthritis, Sydenham’s chorea, erythema marginatum and subcutaneous nodules 2-4 weeks post Strep throat infection
A. Acute Rheumatic Fever - type 2 hypersensitivity to M proteins on Group A Strep
Ix - Jones criteria
Mx - aspirin, steroids, penicillin
Megaloblastic anaemia, may present alongside other autoimmune disease
A. Pernicious anaemia - type 2 hypersensitivity to intrinsic factor and gastric parietal cells
Ix - Anti Gastric Parietal cell Ab/ Anti-IF Ab
Mx - Dietary B12 or IM B12
History of asthma or allergic rhinitis, followed by eosinophilia
A. Churg-Strauss (eGPA) - type 2 hypersensitivity causing medium and small vessel vasculitis
Ix - p-ANCA
Mx - prednisolone, AZA, cyclophosphamide
Presents with sinus problems, lung cavitations and haemorrhage, typically with crescenteric glomerulonephritis
A. Wegener’s (GPA) - type 2 hypersensitivity affecting medium and small vessels
Ix - c-ANCA
Mx - Steroids, AZA, co-trimoxazole
May present with constitutional symptoms, nephritic syndrome and purpura or livedo racemosa (irregular broken circles on skin)
A. Microscopic polyangitis - type 2 hypersensitivity affecting small vessels
Ix - p-ANCA
Mx - steroids, cyclophosphamide
Persistent itchy wheals lasting more than 6 weeks
A. Chronic urticaria - type 2 hypersensitivity to NSAIDs, cold, food, etc.
Ix - challenge test, ESR, skin prick
Mx - avoidance, preventative antihistamine, IM adrenaline if throat swelling
What is the mechanism of type 3 hypersensitivity?
A. IgG or IgM immune complex (soluble Ag) mediated tissue damage
Presents with joint pain, splenomegaly, skin, nerve and kidney involvement. Associated with Hep C.
A. Mixed essential cryoglobulinaemia - type 3 hypersensitivity against hepatitis C antigens
Ix - clinical/ biopsy
Mx - NSAIDs, steroids, plasmaphoresis
Presents with rashes, itching, joint pain, LNpathy, fever and malaise 7-12 days following treatment with certain drugs e.g. penicillins
A. Serum sickness - type 3 hypersensitivity to foreign proteins in antiserum
Ix - low C3, immune complexes in blood
Mx - stop drug, steroids, antihistamines, analgesia
Presents with fever, fatigue, weakness, joint pain, skin, nerve and kidney involvement, pericarditis and MI. Associated with Hep B
A. Polyarteritis Nodosa - type 3 hypersensitivity to HBV/HCV Ag
Presents with 4 of: serositis, seizure, apthous ulcer, arthritis, photosensitivity, discoid rash, malar rash, haematology, kidney involvement
ANA+, anti-dsDNA/anti-SM abs
A. SLE - type 3 hypersensitivity to intracellular components
Ix - low C4, low C3 (marker of active/severe disease), Abs: dsDNA, Ro, La, SM, cardiolipin, raised ESR
Mx - analgesia, steroids, cyclophosphamide
What is the mechanism underlying type 4 (delayed) hypersensitivity disorders?
A. T-cell mediated destruction of cells
Anti-GAD (glutamate decarboxylase) antibodies
A. Type 1 diabetes mellitus - type 4 hypersensitivity
CSF shows oligoclonal bands of IgG on electrophoresis. Treated with INF-B and steroids.
A. Multiple sclerosis - type 4 hypersensitivity to oligodendrocyte proteins (Myelin basic protein, proteolipid protein)
Anti-CCP antibodies are 95% specific for this disease, but not very sensitive (negative result doesn’t exclude disease)
A. Rheumatoid arthritis - type 4 hypersensitivity to antigen in synovial membrane
Rheumatoid Factor is 85% sensitive and aids diagnosis
Reaction to contact with chemicals, poison ivy and nickel
A. Contact dermatitis - type 4 hypersensitivity
Skip lesions which may show transmural inflammation on biopsy, which is gold standard
A. Crohn’s disease -type 4 hypersensitivity
NOD2 mutation in 30%
Mx - mesalazine, steroids, TNF-a antagonists e.g. infliximab
