The bone marrow is an organ, and organs are formed by cells that perform a similar function to a certain degree. The main function of the bone marrow is the production of blood cells whether they are red blood cells, white blood cells or platelets. When a disease affects the bone marrow, the patient usually has abnormalities in the production of such components. Bone marrow biopsy is one of the most commonly ordered hematological investigations because the bone marrow is the main manufacturing plant of blood cells. Since it is hidden under a layer of thick bone, we need special techniques to obtain a sample for investigations. After birth and as the human advances in age, the percentage of the active “red” marrow decreases, and by late childhood and early adulthood, it becomes almost completely replaced by the inactive “yellow” marrow. The active marrow becomes limited to the axial bones, especially the sternum or “breastbone”, ribs, hip bone and the proximal ends of long bones. In other words, the parts near the center of the body.
Bone marrow biopsy is ordered for the following conditions:
- An unexplained anemia, alarmingly decreased platelets or increased white blood cells.
- The diagnosis, staging and monitoring of the treatment of hematological malignancies whether they are leukemias, myelodysplastic disorders, lymphomas or multiple myeloma.
- Fever of an unknown origin.
- Some rare metabolic diseases, such as Nieman-Pick and Gaucher, which are related to the storage of fats and glycogen in our bodies.
- Metastatic cancers from elsewhere in the body and staging of other granulomatous diseases, including sarcoidosis and tuberculosis.
Bone marrow biopsy types
There are two main types of bone marrow biopsies: aspiration biopsy and trephine biopsy.
In bone marrow aspiration, the doctor will push a needle through the thick bone -under local anesthesia-, and then aspirate a small amount of the marrow, this procedure is used in the case of some bone cancers to get a general look on the cellular components of the bone marrow.
Trephine bone marrow biopsy on the other hand involves the sampling of a small part of the bone with the marrow underneath with special needles and technique. It is more accurate than the standard bone marrow biopsy, and the only option in cases where bone marrow aspiration can’t be performed as in cases of aplastic anemia -which is a type of anemia due to the inability of the bone marrow to produce red cells-, and metastatic cancers.
Bone marrow biopsy is usually carried out either in a hospital or an outpatient clinic, and the doctor will usually administer local anesthesia with antianxiety medications.
Bone marrow biopsy results
After the biopsy specimen or aspirate is sent to the lab, results come out:
- To confirm or contradict the diagnosis.
- Stage the disease
- Show response to treatment.
Biopsy results mainly involve the following categories:
Cellularity
This is a general look on the number of cells in the bone marrow. A hypercellular bone marrow can be an indication of cancer or increased peripheral destruction of blood cells with an associated increased production, as in cases of hypersplenism -a condition which involves an enlarged spleen that excessively destroys blood cells-. On the other hand, a hypocellular bone marrow can be seen in aplastic anemia or bone marrow failure.
Cellular components
Which is a specified view on the bone marrow and its different cells. The presence of blast cells is normal in the bone marrow as long as they don’t exceed 20%. Otherwise, it is a sure diagnosis of acute leukemia.
Abnormal components
Some components of a bone marrow biopsy are abnormal and shouldn’t be there, as in cases of hemochromatosis, in which excessive iron is deposited in the marrow. Other examples include Gaucher and Niemann-Pick diseases, in which excessive fat is found, or amyloidosis in which excessive amounts of an abnormal protein called amyloid are deposited in the bone marrow, encroaching on the normal cells.
Immunophenotyping
This type of investigation is directed towards the identification of the source of malignant cells. Bone marrow cancers as leukemia are known to be monoclonal, which means that they originated from a single mother cell, and proving this relationship is enough to both diagnose cancer and to know whether this leukemia is myeloid or lymphoid.
Bone marrow biopsy pain
Pain is a defense mechanism that we developed to protect and alert us against dangers to our bodies. If we understand this, we will realize that in fact, many of our internal organs have no pain receptors. Our brain itself has no pain receptors, but the skin is full of them. In the bone, pain receptors are mainly found on the covering of the bones -scientifically called the periosteum-. So, when the doctor sticks a needle into your bone marrow, it is normal to be extremely painful. The pain is triggered by the bone receptors on the skin, muscles, tendons and periosteum.
However, you will not feel excruciating pain because all bone marrow procedures are done under anesthesia. Pain itself is influenced by many factors such as age, obesity, anxiety and the length of the procedure.
How is pain reduced during the biopsy?
There are several ways to reduce the pain in such procedures. The mainstay of pain reduction is local anesthesia using drugs such as lidocaine. Lidocaine functions to block pain from the skin and the periosteum. Other options include sedation by some antianxiety drugs like lorazepam given intravenously. Your doctor may also give you an opioid analgesic like morphine to block all sensations of pain. These measures ensure that no pain is felt at all. If opioid analgesics are not given, a slight pain may yet be felt when inserting the needle.
It is worth noting, however, that pain reduction technique is not universal, and your doctor will choose the method of pain reduction depending on your situation. Morphine isn’t always a good option and can cause side effects that are worse than the sharp, yet brief pain produced by the needle during aspiration. Your doctor will also talk you through the procedures to decrease your anxiety as much as possible since it is scientifically proven that anxiety is one of the most contributing factors to pain.