Pseudoangiomatous Stromal Hyperplasia (PASH)

What is PASH?

Pseudoangiomatous Stromal Hyperplasia (or PASH) is a type of blood disorder characterized by abnormal growth of bone marrow stem cells in the bone marrow. These stem cells are called mesenchymal stem cells because they originate from mesodermal tissues such as bone marrow, spleen or lymph nodes. Mesenchymal stem cells are the most common type of adult stem cell found in the body. They have been shown to play a role in many different biological processes including immune system development, wound healing, inflammation and cancer. However, these cells do not normally develop into any specific tissue types. Instead they migrate throughout the body where they differentiate into other specialized cells which then become part of various organs and tissues.

The mesenchyme can divide indefinitely but eventually it stops dividing altogether. When this happens, the cells stop producing new blood cells.

This condition is known as chronic granulomatosis.

In some cases, the disease may cause symptoms similar to those caused by leukemia (lymphoma), a form of childhood leukemia. In most cases, however, the disease produces no symptoms at all unless it is very advanced.

What are the types of pseudoangiomatous stromal hyperplasia?

There are two major types of PASH: primary and secondary.

The primary form, also called idiopathic, is the less severe type of the disease and appears to be inherited (genetic). Most of the cases are thought to be caused by a mutation in the JAK2 gene.

The secondary form is a result of an underlying medical condition such as infection with Human Immunodeficiency Virus (HIV), a viral infection that attacks the immune system, or prolonged use of immunosuppressive medication to treat severe allergies or rheumatoid arthritis.

What are the risk factors of PASH?

The risk factors of PASH are not well understood. It is known that people with a weakened immune system or those who have undergone an organ transplantation are more prone to develop PASH.

What are the complications of PASH?

PASH may lead to complications such as low blood counts, which may result in severe anemia (low number of red blood cells), neutropenia (low number of a certain type of white blood cells, called neutrophils), or thrombocytopenia (low number of platelets).

What does a PASH patient look like?

Sources & references used in this article:

Pseudoangiomatous stromal hyperplasia (PASH): a mammary stromal tumor with myofibroblastic differentiation by CM Powell, ML Cranor, PP Rosen – The American journal of …, 1995 – journals.lww.com

Pseudoangiomatous stromal hyperplasia (PASH) of the breast: a series of 24 patients by E Bowman, G Oprea, J Okoli, K Gundry… – The breast …, 2012 – Wiley Online Library

Pseudoangiomatous stromal hyperplasia (PASH): a brief review by SS Jaunoo, S Thrush, P Dunn – International journal of surgery, 2011 – Elsevier