A patient presents with sudden-onset severe lower abdominal pain, nausea, vomiting, and inability to pass urine. On physical examination, there is suprapubic tenderness and a palpable bladder. What is the most likely diagnosis?

Correct Answer: B

Rationale: The patient's presentation with sudden-onset severe lower abdominal pain, nausea, vomiting, inability to pass urine, suprapubic tenderness, and a palpable bladder is classic for acute urinary retention. Acute urinary retention is a urological emergency characterized by the sudden inability to pass urine due to the inability to empty the bladder completely. The palpable bladder on physical examination indicates significant bladder distension. This condition can be caused by multiple factors such as bladder outlet obstruction, neurogenic causes, or medications affecting bladder function. Prompt intervention is necessary to relieve the bladder distension, alleviate symptoms, and prevent complications like bladder rupture.

Correct Answer: C

Rationale: The clinical presentation of fever, malaise, maculopapular rash starting on the face and spreading to the trunk and extremities, along with leukopenia and thrombocytopenia, is highly suggestive of Rocky Mountain spotted fever (RMSF) caused by Rickettsia rickettsii. RMSF is a tick-borne illness transmitted by the American dog tick, Rocky Mountain wood tick, and brown dog tick. The constellation of symptoms described aligns well with the typical presentation of RMSF. Borrelia burgdorferi causes Lyme disease, which presents with erythema migrans but does not typically cause leukopenia or thrombocytopenia. Plasmodium falciparum is the causative agent of severe malaria and would present with symptoms such as cyclic fevers, anemia, and jaundice but not the described rash distribution.

Correct Answer: A

Rationale: The most likely causative agent in this scenario is Plasmodium falciparum, a protozoan parasite that causes malaria. The patient's symptoms of fever, chills, headache, and myalgia align with the typical presentation of malaria. Additionally, the presence of intraerythrocytic ring forms and trophozoites on blood smear examination is characteristic of Plasmodium species, particularly P. falciparum, which causes the most severe form of malaria.

Correct Answer: A

Rationale: In a pregnant woman presenting with severe abdominal pain, syncope, signs of hypovolemic shock, and gestational age of 6 weeks, the most likely cause is an ectopic pregnancy. An ectopic pregnancy occurs when a fertilized egg implants outside the uterus, commonly in the fallopian tube. As the pregnancy grows and the tube stretches, it can lead to rupture, causing severe abdominal pain, internal bleeding, and signs of shock. This is a life-threatening emergency that requires prompt diagnosis and management. It is important to consider ectopic pregnancy in any pregnant woman presenting with abdominal pain and signs of shock, especially in the first trimester.

Correct Answer: C

Rationale: Placenta previa is a condition in pregnancy where the placenta implants low in the uterus, partially or completely covering the cervix. This can lead to painless, bright red vaginal bleeding in the third trimester. However, in some cases, placenta previa can also present with sudden onset of severe lower abdominal pain and signs of shock, such as syncope, pallor, and abdominal distention due to concealed bleeding. In severe cases, the bleeding can be significant and life-threatening for both the mother and the baby. It is important to promptly diagnose and manage placenta previa to prevent complications.