When should a spinal tap be performed and why

What is a bone marrow puncture?

A spinal tap, or bone marrow puncture, consists of the introduction of a fine needle, with a trocar, into the bone marrow cavity, performing an aspirate to extract the blood-forming (hematopoietic) tissue. Figure 1 shows the main operations involved in this process.

The medullary puncture is usually done in the sternum (handle or 3rd intercostal space) and is known as “sternal puncture” (Figure 2), but it can also be done in the iliac crest.

How is the blood selected and what can be analyzed?

Once the extraction is done, the medullary lumps (white colored parts) that are mixed with the blood in the Petri dish must be selected. With the edge of a slide, several not very thick extensions are made on another slide which, when they are well dried, will be stained to observe the cells under the microscope.

Normally the May-Gründwald-Giemsa (MGG) stain is used, but if, in addition, the hematology specialist wants to know the state of the iron deposits in the body and confirm if there is iron deficiency, a Pearls stain can be performed, which will stain the iron stored in the bone marrow blue-green (Figure 3).

MGG staining allows morphological observation of the blood-forming cells or hematopoiesis cells. All blood cells originate from a single cell, the “pluripotent stem cell”, which, through different differentiation processes, will give rise to 2 major mature lines: myeloid and lymphoid, with their corresponding precursors. These, through progressive maturation, will transform into mature cells: leukocytes (granulocytes, lymphocytes and monocytes), red blood cells and platelets (Figure 4).

When is a bone marrow puncture indicated?

The main reasons for performing a bone marrow puncture are summarized below:

  • Pernicious anemia (arregenerative anemia).
  • refractory anemia (myelodysplasia)
  • Gaucher’s disease (thesaurismosis)
  • Erythroblastopenia (thymoma)
  • Monoclonal gammopathy of uncertain significance (MGUS)
  • Hemolysis (regenerative anemia)
  • Malignant histiocytosis (MH)
  • Acquired immunodeficiency (AIDS)
  • Visceral leishmaniasis (Kala-azar)
  • Chronic myeloid leukemia (CML)
  • Chronic lymphocytic leukemia (CLL)
  • Acute myeloid leukemia (AML)
  • Acute lymphoid leukemia (ALL)
  • Lymphoma
  • Idiopathic myelofibrosis (IM)
  • Multiple myeloma
  • Carcinomatous metastasis of the bone marrow
  • Polypectomy vera (PV)
  • Chronic inflammatory syndrome
  • Essential thrombocythemia (ET)

The above mentioned correspond to the following clinical situations:

  1. Anemia of uncertain diagnosis. Anemia or decreased hemoglobin concentration in the blood is one of the causes for performing a bone marrow puncture. Most of the time anemia is due to a lack of iron (iron deficiency anemia) or a lack of vitamins (megaloblastic anemia). In both cases a hemogram will facilitate the diagnosis with the variation of the Mean Corpuscular Volume (MCV) of the red blood cells. Thus, if there is a decrease (MCV
  2. Alteration of blood cells of unknown origin. A bone marrow puncture may be indicated if there are significant alterations in the hemogram, without secondary causes. An example is variations in the number of blood cells affecting one or several cell lines: persistent decreases in granulocytes (leukopenia: 11 x 109/l) or platelets (thrombocytosis: >350 x 109/l). Normally these blood alterations are reactions of the bone marrow to an external stimulus, most of the time without importance but, in other cases, they may be due to a bone marrow disease or hemopathy. In such a case it is essential to perform a bone marrow puncture to observe its condition. Malignant hemopathies include myeloproliferative and lymphoproliferative syndromes (chronic myeloid leukemia, chronic lymphocytic leukemia and lymphomas) and acute leukemias (myeloblastic and lymphoblastic).
  3. Severe pancytopenia or a decrease in all blood cells. This may be a first sign of severe blood disease and an indication for marrow puncture. In some patients with pancytopenia it is impossible to have enough bone marrow material to do a morphological examination, white puncture or “dry-tap”. In such a case, a new marrow puncture can be attempted elsewhere in the sternum or iliac crest, but if the white puncture is redone, a bone biopsy must be performed. This is a histological examination of the marrow which, unlike the aspirate, offers a view of the structure of the bone, and makes it possible to appreciate the actual cellularity and also the possible presence of extra-hematological cells (metastases). With the biopsy, therefore, the diagnosis can be differentiated between bone marrow aplasia (disappearance of blood-forming cells, replaced by fat cells) and idiopathic myelofibrosis or fibrous degeneration of the bone marrow cavities, with the disappearance of normal hematopoiesis. Sometimes a white puncture is due to a non-absolute invasion of the marrow cavities by leukemic cells which, because of their packaging, cannot be aspirated with a bone marrow puncture. In such cases only bone biopsy will allow a diagnosis of acute leukemia with aleukemic leukemia or pancytopenia.
  4. Monoclonal gammopathy. It is the appearance of a peak in the gammaglobulins of the proteinogram. This means an alteration of serum electrophoresis (monoclonal band) and is an indication for a bone marrow puncture to rule out multiple myeloma or plasma cell cancer. The fact that, from the age of 70 years onwards, 5% of people suffer from monoclonal gammopathy of uncertain significance (MGUS) is, together with myelodysplastic syndromes (MDS), a fairly frequent cause of bone marrow aspiration in the elderly.
  5. Splenomegaly or enlargement of the spleen. It is usually due to different causes but, if it appears, a hemopathy should be considered. There are two infrequent causes that are often diagnosed with a spinal tap. One is visceral leishmaniasis or dog-transmitted parasitic disease that causes an accumulation of parasites in bone marrow and spleen. Another is Gaucher’s disease, due to a metabolic disorder, which causes an accumulation of fatty deposits in various tissues, especially in the spleen.
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Preparation required for a bone marrow puncture

The spinal tap does not require any special preparation. All that is needed is a stretcher so that the patient can be stretched face up (sternal puncture) or face down (iliac crest puncture). It is recommended that the test be performed on an empty stomach, in case the patient feels a little dizzy when returning to bed after the procedure.

Although, in principle, the entry of the needle into the cavity of the medulla does not cause pain, penetration into the periosteum is painful, so a local anesthetic is administered subcutaneously. A fine needle with a trocar is used for the puncture and a 2 to 10cm syringe for the aspiration.

Care after a spinal tap

No special care is necessary after a bone marrow puncture, except in patients with a low platelet count (plateletopenia), where precautions should be taken in case of a small hemorrhage (subcutaneous hematoma) after the puncture.

Alternatives to spinal tap

Spinal tap is not a treatment, but a diagnostic procedure. For the time being, just as there is no other technique to observe blood cells than venous puncture, there is no substitute method to observe bone marrow cells without a bone puncture.