NBME 17 Incorrects Questions with Complete
Solutions
What is predictive of a clonal lymphoid proliferation? surface kappa:surface lambda ratio
Each plasma cell can only make either kappa or lambda. Normal ratio about 3:1. If one is much
higher than the other, that means there is MONOCLONAL proliferation (instead of the normal
polyclonal), such as in multiple myeloma
40yo M with extreme sensitivity to sunlight. Exposure to sun causes formation of vesicles and
blisters on skin, which takes weeks to heal. He is diagnosed with a disorder caused by increased
synthesis of compounds in the skin that are subject to excitation by visible light.
What pathway is defective? Heme synthesis
Porphyria cutanea tarda is caused by defect in uroporphyrinogen decarboxylase in heme
synthesis --> accumulation of uroporphyrin 1
Sx: blistering cutaneous photosensitivity caused by hepatotoxic triggers (alcohol, estrogens).
Most common type or porphyria
,6yo boy with recurrent systemic infections with Neisseria meningitidis but healthy otherwise.
What lab test is likely to be abnormal in this child? Total hemolytic complement
concentration
C5-C9 deficiency causes failure of formation of membrane attack complex (MAC) which causes
susceptibility to Neisseria
Missing C3 factor causes what? Recurrent infection by pyogenic bacteria (2/2 lack of
immune complex and pathologic bacterial clearance)
Increased susceptibility to type III hypersensitivity reactions
Missing CD55 causes what? Paroxysmal nocturnal hemoglobinuria
Due to unregulated activation of complements leading to lysis of RBCs
Missing C1 esterase inhibitor causes what? Hereditary angioedema
ACE inhibitors are contraindicated
, Unregulated activation of kallikrein by complement system leading to increased bradykinin
activity
Boy with anemia since birth with splenomegaly. Splenectomy is indicated if the anemia is
caused by which disorders? Hereditary spherocytosis
What cytokines are released to cause fever and inflammation? IL-1 and TNF-a
DIC labs?
PT/INR:
aPTT:
Platelet count:
Fibrinogen:
Fibrin degradation products:
D-Dimer:
Antithromibin III: PT/INR: increased
Solutions
What is predictive of a clonal lymphoid proliferation? surface kappa:surface lambda ratio
Each plasma cell can only make either kappa or lambda. Normal ratio about 3:1. If one is much
higher than the other, that means there is MONOCLONAL proliferation (instead of the normal
polyclonal), such as in multiple myeloma
40yo M with extreme sensitivity to sunlight. Exposure to sun causes formation of vesicles and
blisters on skin, which takes weeks to heal. He is diagnosed with a disorder caused by increased
synthesis of compounds in the skin that are subject to excitation by visible light.
What pathway is defective? Heme synthesis
Porphyria cutanea tarda is caused by defect in uroporphyrinogen decarboxylase in heme
synthesis --> accumulation of uroporphyrin 1
Sx: blistering cutaneous photosensitivity caused by hepatotoxic triggers (alcohol, estrogens).
Most common type or porphyria
,6yo boy with recurrent systemic infections with Neisseria meningitidis but healthy otherwise.
What lab test is likely to be abnormal in this child? Total hemolytic complement
concentration
C5-C9 deficiency causes failure of formation of membrane attack complex (MAC) which causes
susceptibility to Neisseria
Missing C3 factor causes what? Recurrent infection by pyogenic bacteria (2/2 lack of
immune complex and pathologic bacterial clearance)
Increased susceptibility to type III hypersensitivity reactions
Missing CD55 causes what? Paroxysmal nocturnal hemoglobinuria
Due to unregulated activation of complements leading to lysis of RBCs
Missing C1 esterase inhibitor causes what? Hereditary angioedema
ACE inhibitors are contraindicated
, Unregulated activation of kallikrein by complement system leading to increased bradykinin
activity
Boy with anemia since birth with splenomegaly. Splenectomy is indicated if the anemia is
caused by which disorders? Hereditary spherocytosis
What cytokines are released to cause fever and inflammation? IL-1 and TNF-a
DIC labs?
PT/INR:
aPTT:
Platelet count:
Fibrinogen:
Fibrin degradation products:
D-Dimer:
Antithromibin III: PT/INR: increased
