Immune diseases

Question 1

erythema multiforme (EM)

Answer 1

• acute inflammatory disorder that can involve the skin of the extremities, face, trunk, and neck.
• Severe cases (EM major) can also affect oral mucous membranes and the tongue.
• The appearance of EM can vary, but patients typically develop erythematous, round papules that evolve into target lesions with a dusky central area, a dark red inflammatory zone surrounded by a pale ring, and an erythematous halo in the lesion’s periphery.
• represents a cell-mediated immune process, with an inflammatory infiltrate predominated by cytotoxic CD8+ lymphocytes.
• most frequently associated with infections (especially herpes simplex virus and mycoplasma) and may be due to an immune response against antigens deposited in the skin.
• can also be seen in association with certain medications (eg, sulfonamides), malignancy, and collagen vascular diseases.

Question 2

Stevens-Johnson syndrome

Answer 2

• characterized by rapid onset of erythematous macules with necrosis and skin sloughing.
• Systemic signs (eg, fever, hypotension) are common.
• may also cause target lesions, but it is usually associated with medications (eg, sulfonamides, allopurinol, phenytoin).

Question 3

chronic granulomatous disease (CGD)

Answer 3

• recurrent bacterial and fungal infections due to impaired intracellular killing by phagocytes
• caused by a genetic defect in the NADPH oxidase complex.
• NADPH oxidase normally functions to transfer an electron from NADPH to oxygen, resulting in the production of superoxide (O2•-) and subsequent formation of other reactive oxygen species such as hydroxyl radicals (HO•) and hydrogen peroxide (H2O2).
• These oxidants have direct microbicidal activity and also function to activate granule proteases (eg, elastase, cathepsin G) that destroy engulfed pathogens.
• Most microorganisms produce hydrogen peroxide as a waste product of metabolism
• Catalase-negative organisms are unable to prevent the accumulation of hydrogen peroxide within phagosomes, which allows the phagocytes to generate potent microbicidal agents (eg, hypochlorite) even when host superoxide production is impaired

Question 4

Guillain-Barré syndrome (GBS).

Answer 4

• patient with progressive lower extremity weakness, depressed deep tendon reflexes, and paresthesias
• group of immune-mediated demyelinating polyneuropathies that are thought to be caused by molecular mimicry.
• antecedent event (typically an infection) provokes an immune response that cross-reacts with the Schwann cells and myelin sheath of the peripheral nerves
• myelin sheath is stripped from the axon, leading to loss of neuronal conductivity and axonal degeneration.
• up to 1/3 of GBS cases are preceded by C. jejuni infection = common cause of acute (sometimes bloody) diarrhea
• experience symmetric, ascending weakness that begins in the legs and progresses to flaccid paralysis and resp failure.
• decreased or absent DTR, paresthesia, pain (often of the back) and dysautonomia are common