A 7 year old boy presents with a low-grade fever, arthralgias, colicky abdominal pain, and a palpable purpuric rash limited to the lower extremities. Laboratory studies reveal a guaiac-positive stool, a urinalysis with red blood cell (RBC) casts, hematuria, and mild proteinuria, and a CBC with a normal Hb, Hct, and platelet count. Which of the following is the most likely diagnosis?

Correct Answer: D

Rationale: Henoch-Schonlein purpura (HSP) presents with purpuric rash, arthralgias, abdominal pain, and glomerulonephritis (RBC casts), typically in children.

Correct Answer: C

Rationale: Veins carry deoxygenated blood back to the heart, except for the pulmonary vein which carries oxygenated blood.

Correct Answer: A

Rationale: Shortness of breath and dry cough may indicate pulmonary toxicity, a serious adverse effect of amiodarone.

Correct Answer: A

Rationale: Hypokalemia increases the risk of digoxin toxicity, requiring prompt correction.

Correct Answer: A

Rationale: The heart is composed of cardiac muscle tissue, enabling it to contract and pump blood.