From: Sunil []
Sent: Friday, May 22, 2020 08:30:17 PM






Heriditary spherocytosis

The following article covers most of the important points about Hereditary spherocytosis (HS) that are tested in the USMLE exam. Pay close attention to bold phrases as they are key points that appear in the exam as questions/hints.

HS is a common inherited hemolytic anemia resulting from abnormalities in the proteins of the red blood cell (RBC) membrane (mainly spectrin but also ankyrin, protein 4.2, and band 3).  

It is usually inherited in an autosomal dominant pattern, is most common in whites of Northern European descent, and is infrequent in African Americans. (Hereditary elliptocytosis (HE) is another disorder of the red cell membrane that is a common cause of inherited hemolytic anemia in African Americans.)

The membrane abnormalities of HS cause fragility of the red cell membrane with loss of surface area and a resultant spheroid shape instead of the normal biconcave appearance. The MCV is usually within the normal range for age, but may be slightly elevated if there is a brisk reticulocytosis. MCHC is high due to the relative cellular dehydration.

The abnormal RBCs become trapped in the spleen where they are eventually hemolyzed (so-called extravascular hemolysis).

This leads to an increase in LDH, unconjugated bilirubin.

Haptoglobin is a scavenger hor free hemoglobin and is normal or decreased in HS (as the hemolysis is extravascular).

Osmotic fragility is increased in HS.

Splenectomy is a common treatment but should be delayed until after school going age, if possible, due to the risk of pneumococcal sepsis. Penicillin prophylaxis is recommended for at least the first 5 years after splenectomy with some doctors recommending treatment for life.

Pseudostrabismus vs strabismus

Patients with epicanthal folds can sometimes appear to have esotropia (convergent strabismus) but have normal eye alignment. Their corneal light reflex and cover tests are normal. In addition to epicanthal folds, wide nasal bridge and narrow-set eyes can also give the illusion of esotropia as less sclera is visible in the nasal aspect of both eyes.

Pseudostrabismus can easily distinguished form strabismus by looking at the patient's corneal light reflex. The patient in the picture below has true strabismus as evident by presence of corneal light reflex in different parts of the cornea.

(image modified from Wikipedia:

Clavice Fracture

Clavicle is the bone most commonly fractured during labor and delivery. Although difficult delivery of the shoulder, or extended arms in breech deliveries increase the chances of a clavicle fractures, they can be present even with a history of a normal delivery.

Diagnosis: In addition to delivery history the following features may point towards the diagnosis:
-Decrease/assymetric movement of the limbs. (This may be evident by presence of an assymetric Moro's reflex)
-Palpable crepitus or bony irregularity early on
-A large callus forms quickly and is generally palpable by age 1 week.

Prognosis is excellent. Treatment, if any, is limited to immobilization of the arm and shoulder on the affected side (simply pinning the sleeve to the side of the infant's shirt does the trick). Figure of 8 bandages are no longer used.

Differential diagnosis: Congenital pseudoarthrosis of the clavicle

This condition presents as a palpable lump in the center of the clavicle that does not change or heal with any amount of time. Its cause is unknown. The condition is more common on the right side and generally does not lead to any functional impairment. Surgery is rarely indicated.