In polycythemia vera, there are increased blood cell levels due to overproduction by the bone marrow, which is a soft tissue found within the bones.
Normally, about 45% of the total blood volume is made up of erythrocytes, or red blood cells, and their main function is to carry oxygen to tissues and bring carbon dioxide to the lungs so it can be expired. This value is called the hematocrit.
In polycythemia vera there’s an increase in red blood cell production.
It typically begins with a mutation in a single hematopoietic stem cell, which gives rise to red blood cells, white blood cells, and platelets.
In 90 percent of the affected individuals there is a mutation of the Janus Kinase 2 or JAK2 gene.
Normally, the kidneys produce erythropoietin which is a hormone that binds to receptors on the hematopoietic stem cells and activates JAK2 gene.
When that happens, it causes the cell to divide and thus produce more blood cells.
However, when there’s a mutation, it keeps JAK2 gene activated, and these cells are able to divide even in the absence of erythropoietin.
The mutated cells proliferate, and rapidly become the predominant hematopoietic cells in the bone marrow.
In time these cells start to die out and that’s when scar tissue forms.
At that point, the bone marrow can no longer produce blood cells, leading to anemia or low red blood cell levels, thrombocytopenia or low platelet levels, and leukopenia or low white blood cell levels. This is known as the spent phase.
And once the disease is in the spent phase, it’s really a different disease altogether - at that point it’s myelofibrosis.
The most common symptoms of polycythemia vera are fatigue, dizziness, increased sweating, redness in the face, blurred vision, and itchy skin especially after a hot shower.
Itchiness develops due to the increased number of basophils and mast cells which contain histamine that causes itching when released.