Why would you wash red cells for patients with PNH?

Q. I’m currently doing my rotations at Children’s Memorial Hospital’s blood bank and I was reading the standard operating procedure for washing red cells. One of the conditions in which they need to be washed is paroxysmal nocturnal hemoglobinuria. Do you know why this is?

A. The reason for washing red cells for people with PNH is to get rid of any ABO incompatible plasma.

In a person without PNH, ABO incompatible plasma doesn’t cause any perceptible hemolysis. The antibodies in the donor unit probably just get diluted out enough that they don’t have much of an effect. Or perhaps they get sopped up by other ABO antigens on other cells (did you know that you have A and B antigens on cells besides red cells?! Weird.).

But patients with PNH are super susceptible to complement-induced red cell destruction. They lack the ability to anchor certain proteins (including proteins that protect the red cell against complement) to the red cell membrane. Patients with PNH have a hard time down-regulating even a small amount of complement activation – so theoretically, a transfusion of even a small amount of non-ABO compatible plasma could lead to hemolysis. There have been a few cases of hemolytic transfusion reactions in patients with PNH that have been attributed to this phenomenon…so in 1948, blood banks began washing red cells before giving them to patients with PNH.

However, this practice has been called into question. The Mayo Clinic reviewed 38 years of experience with transfusing patients with PNH, and only found one documented episode of post-transfusion hemolysis). Their conclusion was that the important thing is to use group-specific blood products for patients with PNH; washing seems to be an unnecessary precaution.

Primary CNS lymphoma: a tumor that preys on the immunosuppressed

Here’s another primary CNS tumor that arises in the brain parenchyma: primary CNS lymphoma.

Definition

Just to clarify the word “primary” here – these are lymphomas that arise right in the brain itself. You can also have a lymphoma that arises elsewhere in the body that secondarily spreads to the brain parenchyma. This is exceedingly rare (usually, if lymphoma spreads to the CNS, it just involves the CSF or very superficial areas of the brain). Weird: lymphoma arising in brain parenchyma rarely spreads elsewhere, and lymphoma arising elsewhere rarely spreads to the brain parenchyma.

Most primary CNS lymphomas are B-cell in nature; diffuse large B-cell lymphoma is the most common type. In patients who are immunosuppressed, as you might expect, the tumor cells are usually are positive for Epstein-Barr virus.

Incidence

This is a rare tumor, overall: it accounts for 2% of all extra-nodal lymphomas, and only 1% of intracranial tumors. However, in immunosuppressed patients (like patients with AIDS, or patients who have had a transplant), it is the most common tumor of the CNS.

Gross appearance

Grossly, primary CNS lymphoma is usually multifocal within the brain; it can involve both deep gray matter and white matter. There’s often a lot of necrosis.

Morphology

Here’s a weird thing: the tumor cells tend to accumulate around blood vessels, like this:

Here’s another weird thing: if you stain a section of tumor with reticulin, you’ll often see little reticulin fibers forming “hoops” in between the tumor cells:

Prognosis

This is not a nicely-behaving tumor. Compared to regular lymphoma, primary CNS lymphoma is more aggressive, with a worse response to chemotherapy.