Which of the following imaging modalities is most appropriate for evaluating suspected pulmonary embolism (PE) in a pregnant patient?

Correct Answer: C

Rationale: In a pregnant patient with suspected pulmonary embolism (PE), the most appropriate imaging modality for evaluation is contrast-enhanced computed tomography (CT) pulmonary angiography. This imaging technique has been shown to be safe for the fetus when necessary, especially if the benefits of making a diagnosis outweigh the minimal risks associated with radiation exposure. It provides quick and accurate detection of PE with high sensitivity and specificity.

Correct Answer: D

Rationale: The clinical presentation of a patient with chronic kidney disease (CKD) presenting with weakness, anorexia, confusion, severe anemia, low reticulocyte count, elevated serum creatinine, and decreased erythropoietin levels is most consistent with renal failure-associated anemia. In CKD, the kidneys are unable to produce adequate amounts of erythropoietin, a hormone responsible for stimulating red blood cell production in the bone marrow. The decreased erythropoietin levels lead to a state of anemia, characterized by low hemoglobin levels and subsequent symptoms of fatigue and weakness. The anemia in renal failure is typically normocytic and normochromic. Additionally, the elevated serum creatinine in this patient is a hallmark of kidney dysfunction.

Correct Answer: B

Rationale: Thrombotic thrombocytopenic purpura (TTP) is a rare blood disorder characterized by microangiopathic hemolytic anemia, thrombocytopenia, fever, neurological abnormalities, and renal dysfunction. The peripheral blood smear in TTP typically shows fragmented red blood cells (schistocytes) due to mechanical destruction within small blood vessels. Laboratory findings in TTP commonly include elevated lactate dehydrogenase (LDH), decreased haptoglobin (as it is consumed in the clearance of free hemoglobin), and increased indirect bilirubin due to increased red blood cell breakdown. This combination of clinical presentation and laboratory abnormalities is classic for TTP. Hemolytic uremic syndrome (HUS) may present similarly but is more commonly associated with renal dysfunction and is often triggered by infection with Shiga toxin-producing E. coli.

Correct Answer: B

Rationale: The symptoms described in the patient, such as tremors, rigidity, bradykinesia (slow movement), and postural instability, along with the presence of a shuffling gait, stooped posture, and masked facies, are classic features of Parkinson's disease. These motor symptoms are primarily caused by the degeneration of dopamine-producing neurons in the substantia nigra region of the brain. This results in an imbalance of neurotransmitters, particularly dopamine, leading to motor dysfunction and characteristic movement abnormalities seen in Parkinson's disease.

Correct Answer: B

Rationale: The symptoms described - gradual-onset weakness, spasticity, hyperreflexia, positive Babinski sign, and demyelinating plaques in the white matter of the brain and spinal cord - are indicative of multiple sclerosis (MS). MS is an autoimmune disease where the body's immune system attacks the myelin sheath, leading to the formation of plaques in the central nervous system. The characteristic symptoms of MS include weakness, spasticity (stiffness in muscles), hyperreflexia (exaggerated reflex responses), and positive Babinski sign (upward movement of the big toe). While ALS (Amyotrophic lateral sclerosis) presents with progressive muscle weakness and atrophy without sensory involvement and demyelinating plaques, Guillain-Barré syndrome (GBS) is typically an acute inflammatory demyelinating polyneuropathy affecting peripheral nerves rather than the central nervous system, and myast