A 40 year old patient presented with macrocytic anemia.
- WBC: 8.6 K/uL Normal
- RBC: 3.60 M/uL Decreased
- Hb : 13.1 g/dl Normal
- MCV: 111.3 fl Increased
- MCH: 36.4 pg Increased
- MCHC: 32.7 Normal
- RDW: 15.5% Increased
- Platelet: 360 K/uL Normal
Review of peripheral smear showed several stomatocytes (Figures 1-3).
Serum vitamin B12 and folate levels were normal and serum iron studies were consistent with anemia of chronic disease. Typically anemia of chronic disease is normocytic normochromic. Based on presence of numerous stomatocytes and macrocytosis (which can be seen in patients with hereditary stomatocytosis) it was recommended that patient be investigated for hereditary stomatocytosis and acquired causes of stomatocytosis.
“Stomatocyte” describes the appearance of red blood cells (RBCs) on the peripheral blood smear. Stomatocytes (also called hydrocytes) contain a mouthlike or slitlike pattern that replaces the normal central zone of pallor.
Mechanism of stomatocyte formation — When the normal biconcave disc becomes a uniconcave cup red blood cell (RBC) will appear as a stomatocyte on the peripheral blood smear. There are several mechanisms by which this change can occur:
- In hereditary stomatocytosis (HSt), the mechanism of stomatocyte formation often involves changes in cell volume caused by reduced intracellular ion content.
- In most cases of acquired stomatocytosis and rare inherited conditions that affect lipid metabolism formation often involves either a decrease in RBC membrane surface area or qualitative changes in the composition of the membrane lipid bilayer.
DISORDERS WITH STOMATOCYTES ON PERIPHERAL BLOOD
- Hereditary stomatocytosis (HSt) is an inherited autosomal dominant condition characterized by an excess of stomatocytes Patients have variable degrees of hemolysis and anemia. Hereditary stomatocytosis (HSt) is a rare disorder that presents with various degrees of hemolytic anemia and abnormal red blood cell (RBC) morphology. The genetic abnormalities responsible for these conditions remain incompletely characterized. Some of the defects associated with this condition involve membrane transporters such as Piezo1, Gardos, Rhesus antigen-associated glycoprotein, and the anion exchanger band 3.
- Several rare inherited defects affecting membrane lipid composition have been reported to have stomatocytosis on the peripheral blood smear.
- Tangier’s disease
- Rh null disease
- Liver disease/medications. Stomatocytes can be seen with some acquired conditions such as chronic liver disease (most often due to alcoholism) or acute alcohol intoxication. The stomatocytosis with acute alcohol intoxication appears to be transient, and it may affect a significant proportion of RBCs. The mechanism is thought to be due to a reduction in RBC membrane surface area rather than an increase in RBC volume. Also, dministration of some medications can cause transient stomatocytosis. This was demonstrated in a study that demonstrated formation of stomatocytes upon exposure of RBCs to drugs like vinblastine and chlorpromazine. Intercalation of the drug into the inner half of the lipid bilayer may be responsible for creating the abnormal morphology.
- In some healthy individuals, stomatocytes occasionally can be found on the peripheral blood smear. This is thought to be due to a drying artifact; hence, it is important to evaluate several different areas of the peripheral smear before determining that a patient has circulating stomatocytes.
Hereditary stomatocytosis (HSt)
HSt can be completely asymptomatic or can present with chronic hemolytic anemia of varying severity. The age of presentation depends on the specific gene mutation, presence of other inherited conditions, and other environmental factors. The increasingly routine use of the complete blood count (CBC) in asymptomatic individuals has resulted in earlier diagnosis in some individuals who otherwise might never have come to medical attention. There does not appear to be a relationship between the degree of peripheral stomatocytosis on the blood smear and the severity of hemolytic anemia
The diagnosis of HSt is made by demonstrating the presence of anemia associated with the characteristic changes in RBC morphology (stomatocytosis) in conjunction with altered RBC indices and osmotic fragility. Genetic testing for PIEZO1 or Gardos channel mutations is confirmatory but not required.
The evaluation for HSt includes review of the complete blood count (CBC) and peripheral blood smear, which may show stomatocytes.The blood smear should be reviewed closely to ensure there are no abnormalities of white blood cells (WBCs) or platelets. The RBC indices typically show an increased mean corpuscular volume (MCV) in the range of up to 140 femtoliters (fL) and abnormally low or high mean corpuscular hemoglobin concentration.
-Neerja Vajpayee, MD, is an Associate Professor of Pathology at the SUNY Upstate Medical University, Syracuse, NY. She enjoys teaching hematology to residents, fellows and laboratory technologists.