Review Question - QID 213500

This patient with neurological symptoms and a peripheral blood smear indicating megaloblastic anemia most likely has a vitamin B12 deficiency, which can be caused by infection with Diphyllobothrium latum.

Vitamin B12 deficiency causes a megaloblastic anemia due to decreased synthesis of DNA. The presentation of vitamin B12 deficiency includes neurological symptoms of numbness and paresthesias, as well as symptoms of anemia (e.g. fatigue and pallor). A peripheral blood smear of a patient with vitamin B12 deficiency will show red blood cell macrocytosis as well as hypersegmented polymorphonuclear cells (Illustration A). Diphyllobothrium latum is a tapeworm in humans that absorbs the majority of the host’s vitamin B12 intake in the intestine and can thus lead to vitamin B12 deficiency. Humans can become infected with Diphyllobothrium latum through the ingestion of parasite larvae in raw freshwater fish.

Figure/Illustration A shows a peripheral blood smear in a patient with megaloblastic anemia, featuring a hypersegmented polymorphonuclear cell (arrow in Illustration A).

Incorrect Answers:
Answer 2: Echinococcus granulosus is a tapeworm acquired through the ingestion of eggs in food contaminated with dog feces and leads to hydatid cysts in the liver.

Answer 3: Naegleria fowleri is a protozoan parasite that can be transmitted to humans who swim in warm freshwater and causes a rapidly fatal meningoencephalitis.

Answer 4: Schistosoma haematobium is a parasitic fluke that is transmitted to humans through contact with contaminated fresh water. Chronic infection can lead to squamous cell carcinoma of the bladder.

Answer 5: Schistosoma mansoni is a parasitic fluke that is transmitted to humans through contact with contaminated fresh water and can cause hepatosplenomegaly and portal hypertension.

Bullet Summary:
Vitamin B12 deficiency can be caused by infection with Diphyllobothrium latum.