20-year-old swimmer who has been in excellent health and takes no chronic medications, for new-onset severe fatigue and left upper abdominal pain. She was treated 2 days ago in hospital for presumed typhoid with cefotaxime. She also had past h/o typhoid in 2 yrs back. On physical examination her hea rate of 120 bpm and a palpable spleen. Stool is negative for heme. Lab investigations shows hemoglobin of 5 g/dL with normal TLC and platelets. Peripheral blood smear reveals an excess of spherocytes. All of the following can cause similar type of this condition except:

**Core Concept**
The patient's presentation of severe fatigue, left upper abdominal pain, tachycardia, splenomegaly, and hemolytic anemia with spherocytes suggests a diagnosis of autoimmune hemolytic anemia (AIHA) or Evans syndrome. The recent history of typhoid and cefotaxime treatment may have triggered this condition.

**Why the Correct Answer is Right**
The patient's clinical presentation is consistent with AIHA, which is characterized by the production of autoantibodies against red blood cells (RBCs), leading to their premature destruction. The presence of spherocytes on peripheral blood smear further supports this diagnosis. Spherocytes are small, round RBCs that lack the central pallor, resulting from the loss of membrane surface area due to the removal of the overlying red blood cell membrane.

**Why Each Wrong Option is Incorrect**
**Option A:** Autoimmune hemolytic anemia (AIHA) can be caused by various factors, including infections, medications, and autoimmune disorders. Therefore, AIHA is a plausible diagnosis in this patient.
**Option B:** Thrombotic thrombocytopenic purpura (TTP) is a disorder characterized by the formation of blood clots in small blood vessels throughout the body, leading to microangiopathic hemolytic anemia, thrombocytopenia, and renal failure. While TTP can cause hemolytic anemia, it typically presents with thrombocytopenia, renal failure, and neurological symptoms, which are not mentioned in the patient's presentation.
**Option C:** Hemolytic uremic syndrome (HUS) is a disorder characterized by the formation of blood clots in small blood vessels throughout the body, leading to microangiopathic hemolytic anemia, thrombocytopenia, and renal failure. While HUS can cause hemolytic anemia, it typically presents with thrombocytopenia, renal failure, and neurological symptoms, which are not mentioned in the patient's presentation.
**Option D:** Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disorder characterized by the destruction of RBCs, leading to hemolytic anemia. PNH typically presents with episodic hemoglobinuria, fatigue, and thrombosis, which are not mentioned in the patient's presentation.

**Clinical Pearl / High-Yield Fact**
The presence of spherocytes on peripheral blood smear is a classic finding in autoimmune hemolytic anemia (AIHA). Spherocytes are small, round RBCs that lack the central pallor, resulting from the loss of membrane surface area due to the removal of the overlying red blood cell membrane.

**Correct Answer:** B, C, D. All of the following can cause similar type of this condition except: Thrombotic thrombocytopenic purpura (TTP), Hemolytic uremic syndrome (HUS), Paroxysmal nocturnal hemoglobinuria (PNH).

✓ Correct Answer: D. Infectious mononucleosis