systemic mastocytosis

Diagnosis of mast cell diseases

There seems to be a lot of confusion regarding diagnosis of mast cell diseases, so I figured I’d do a review.

Cutaneous mastocytosis (CM) is diagnosed by skin biopsy.  Urticaria pigmentosa (UP), also called maculopapullar cutaneous mastocytosis (MPCM), diffuse cutaneous mastocytosis (DCM) and telangiectasia macularis eruptive perstans (TMEP) are types of cutaneous mastocytosis.  They each present with a rash and may have accompanying systemic symptoms. 
Mastocytoma of the skin is also diagnosed by skin biopsy.
Systemic mastocytosis (SM) has the following diagnostic criteria:
Major:
1.       Multifocal, dense infiltrates of mast cells (15 or more in an aggregate) detected in sections of bone marrow and/or extracutaneous organ. 
Minor:
1.       In biopsy sections, more than 25% of mast cells in infiltrated area are spindle-shaped or have atypical morphology; or, of all mast cells in bone marrow aspirate smears, more than 25% are immature of atypical. 
2.       Detection of Kit mutation at codon 816 in bone marrow, blood or other extracutaneous organ.
3.       Mast cells in bone marrow, blood or other extracutaneous organ that co-express CD117 with CD2 and/or CD25.
4.       Serum total tryptase persistently >20 ng/mL (if there is not a clonal myeloid disorder.)
SM is diagnosed if a patient has either one major and one minor criteria, or three minor criteria.  So let’s look at how this plays out.
A patient with mast cell symptoms gets a bone marrow biopsy.  It shows more than 25% abnormal mast cells in the section.  They are CKIT negative, have a serum tryptase of 2, and do not express CD2/CD25.  They are diagnosed with SM.
A patient has a biopsy that does not show dense infiltrates.  All their mast cells are shaped normally.  In blood tests, their mast cells are found to express CD2.  They are CKIT+, also from blood.  Their serum tryptase is 28.  They are diagnosed with SM.
A patient has a biopsy that shows dense infiltrates, but they have less than 25% abnormal mast cells and their mast cells do not express CD2/CD25.  They are CKIT- and have a serum tryptase of 18.  They are not diagnosed with SM.
A few things to keep in mind:
Most people with SM are diagnosed by bone marrow biopsy, but a biopsy from any non-skin organ showing mast cell infiltration as described above can be used.  This means if you have a positive lung biopsy, liver biopsy, whatever, you may not necessarily need a bone marrow biopsy. 
It can take up to six bone marrow biopsies to diagnose SM in a patient who has had it the entire time.  This is because there is no way to know where the mast cells will cluster.  A negative bone marrow biopsy does not necessarily mean that you do not have SM.  Hence the minor criteria.
The CKIT test looks for a specific mutation, the D816V mutation.  There are other mutations found in codon 816.  You may have a mutation but test CKIT- because you do not have the D816V mutation.  Also, the blood test for CKIT is not always reliable.  The test way to test this is from a bone marrow sample.  You could test CKIT- in blood and then test CKIT+ in bone marrow.
The serum tryptase criterion refers to persistent baseline level tryptase, not reaction level tryptase. 
So let’s say you have a negative bone marrow biopsy and a blood test that shows you are CKIT+ and have mast cells expressing CD2/CD25.  What do you have?  You have monoclonal mast cell activation syndrome (MMAS.)  MMAS is diagnosed in patients who have one or two of the minor criteria for systemic mastocytosis.
Let’s say you have a negative bone marrow biopsy and blood work that shows normal mast cells and tryptase below 20, but you have systemic symptoms.  What do you have?  You probably have MCAS (mast cell activation syndrome.)  There are some other tests for that.  24 hour urine tests are usually done to measure the levels of histamine metabolites and prostaglandin D2 metabolites.
The following are the diagnostic criteria for MCAS:
1.       Episodic symptoms consistent with mast cell mediator release affecting two or more organ systems: skin (urticarial, angioedema, flushing); GI (nausea, vomiting, diarrhea, cramping); cardiovascular (fainting or near fainting due to low blood pressure, rapid heartbeat); respiratory (wheezing); naso-ocular (itching, nasal stuffiness, red eyes.)
2.       A decrease in frequency or severity; or resolution of symptoms with antihistamines, leukotriene inhibitors or mast cell stabilizers.
3.       Evidence of elevation of urinary or serum marker of mast cell activation: Documentation of elevation of marker during a symptomatic period on at least two occasions, or if baseline tryptase is persistently above 15 ng.  This includes urinary histamine and prostaglandin D2.
4.       Clonal and secondary disorders of mast cell activation ruled out.
MCAS is a diagnosis of exclusion.  It is the diagnosis you receive if you have mast cell symptoms that are ameliorated with mast cell medications if you do not meet the criteria for any other mast cell disease.
Back to SM.  Let’s say you’re positive for SM.  Now what?
They will determine if you have other important markers of disease severity.  These are called B and C findings.  They are as follows:
B findings:
1.       Increased mast cell burden (>30% mast cell aggregates on bone marrow biopsy and/or serum tryptase >200 ng/ml).
2.       Hypercellular marrow, signs of overproduction or abnormal development of blood cells, normal or slightly abnormal blood counts that are not abnormal enough to be considered an associated hematologic disorder.
3.       Swelling of the liver that can be felt manually, no free fluid or signs of dysfunction, persistently swollen glands, swelling of the spleen that can be felt manually without signs of dysfunction.
If you have two or more B findings, you have SSM (smoldering systemic mastocytosis.) 
C findings:
1.       Unusual blood counts (low ANC, low Hb, low platelets)
2.       Swelling of the liver that can be felt manually, with impaired liver function, free fluid and/or portal hypertension.
3.       Large osteolytic lesions and/or pathological fractures.
4.       Swelling of the spleen with impaired function.
5.       Malabsorption with weight loss and/or low albumin.
If you have one or more C finding, you have ASM (aggressive systemic mastocytosis.)
How are these B and C findings identified?  Bone marrow biopsy, blood tests and imaging (ultrasounds, MRI, etc.) 
If you have SM and one B finding, or no B findings, you have indolent systemic mastocytosis (ISM.) 
If your bone marrow biopsy shows significant overproduction or abnormal development of a cell type that is not a mast cell, you may be diagnosed with SM-AHNMD (systemic mastocytosis with associated hematologic non-mast cell lineage disease.)  People with this type of SM also have another blood disorder, such as chronic myelogenous leukemia, myelodysplasia, etc.  In these patients, serum tryptase is not reliable to assess mast cell burden.  
Mast cell leukemia (MCL) is extremely rare.  It is diagnosed by >20% mast cells on the bone marrow aspirate smear.   
Mast cell sarcoma is a very aggressive form of sarcoma.  It is diagnosed by biopsy of the tumor.  People with these tumors quickly developed mast cell leukemia.  There have only been three cases reported in literature.  To be clear, this is NOT the same as mastocytoma.  Mastocytomas are benign.
I think I got everything.  Any questions?  Ask in the comments.

Mast cell disease in families

Three types of MCAD are currently known: systemic mastocytosis (SM); mast cell activation syndrome (MCAS); and mast cell leukemia (MCL).  SM and MCL are thought to be rare, while MCAS is now believed to be much more common, and possibly even the underlying cause of various clinical presentations (such as IBS and fibromyalgia.)  Very little is known about the heritability of these conditions , but many patients report that they have family members with similar symptoms. 

A study examining the familiality of MCAD found that 74% of patients interviewed had at least one first degree relative (parents, siblings, children) with systemic MCAD, regardless of MCAD subtype or gender.  The prevalence of systemic MCAD among first-degree relatives was 46%, while the prevalence in the control group is about 17%.  The prevalence of MCAD among first-degree relatives of patients with MCAS was 60%; with SM was 44%. 


MCAD subtype and severity of symptoms varied between family members.  Variable genetic alterations in CKIT were detected.  Activating CKIT mutations were found in 65% of patients, compared to 15% of the control group. The genetic mutations detected in the three families included mutations at position 816 of CKIT (D816G, D816V, S1A).  This finding is remarkable in that it disproves the longstanding belief that the somatic nature of KIT and related exon 17 mutations means that it cannot be inherited.  It also supports the belief that other mutations in genes that regulate mast cells could be contributing to these diseases.  Multiple mutations were sometimes found in the same patient, including those found in other genes (JAK2, TET2, DNMT3A, ASLX1, CBL, U2AF1, SRSF2, MS4A2). 


There was also no obvious relation between the CKIT mutations and clinical severity of MCAD.  Although familial occurrence due to shared environmental factors cannot be ruled out, it is likely that there is a significant genetic contribution to this phenomenon.  More females than males were affected.  The prevalence of MCAS was expected to be at least within the single-figure percentage range in the population (1-9%.) 


Systemic MCAD family histories include more systemic MCAD cases than would be expected when compared to the prevalence in the general population. This study advocates that the different subtypes of MCAD (MCAS and SM) should be more accurately regarded as varying types of the same disease rather than distinct diseases of mast cell dysfunction.


Reference:

Molderings GJ, Haenisch B, Bogdanow M, Fimmers R, No¨ then MM (2013) Familial Occurrence of Systemic Mast Cell Activation Disease. PLoS ONE 8(9):e76241. doi:10.1371/journal.pone.0076241

Bone marrow biopsy

Most people with suspected systemic mastocytosis receive a bone marrow biopsy as part of their diagnostic testing.  Sometimes people will have confirmed mast cell infiltration in another organ, in which case a bone marrow biopsy may not be needed. 
I know that once I needed a bone marrow biopsy, I sort of felt like my illness had hit the big time.  Like it was time to be really concerned.  My family and friends were really concerned because bone marrow biopsies are used to diagnosis serious diseases.  It is okay to be scared.  But the procedure was not even close to the worst I’ve had, and the pain was manageable. 
In the middle of long bones, there is a squishy center called bone marrow.  Your bone marrow produces most of your body’s blood cells.  The marrow is essentially organized tissue that holds the immature blood cells.
Red bone marrow is active and produces red blood cells, platelets, neutrophils, basophils, eosinophils, monocytes/macrophages, T cells, B cells and mast cells.  Yellow bone marrow mostly contains fat.  Red bone marrow is found in flat bones, like the sternum (breast bone) and the pelvic girdle (upper hip bones.)  In children, the femur (thigh bone) also contains red marrow.
A bone marrow biopsy removes some of the solid tissue from the red marrow to look for abnormal cells.  It uses a long, hollow needle.   Using this needle, a solid piece of bone marrow is removed.  This is called a core. 
A bone marrow aspiration, which removes some liquid from the red marrow, is often done at the same time.  It uses a syringe to remove a little bit of the liquid. 
When you arrive, you may be given IV sedation.  You usually have to request this in advance.  Generally, this is “twilight sedation,” in which you are awake but given medications to relax and manage the pain. 
If they are taking samples from the back of your pelvic crest, you lay on your stomach.  You receive a local anesthetic, typically lidocaine.  It will burn as the drug numbs the area.  (I’ve always found it really ironic that an anesthetic burns.)  A small incision is made in the skin at the biopsy site. 
A hollow needle is then pushed through the bone and into the marrow.  A syringe is attached to the needle and the person doing the procedure pulls back on the plunger to draw liquid into the needle.  This is called the aspirate.  When the aspirate is removed, it changes the pressure inside the bone and causes some pain.  Sometimes no aspirate is found.  This is called a “dry tap.”  If this occurs, another site is biopsied. 
After the aspiration, the biopsy is performed.  This uses a larger hollow needle that is pushed through the bone and into the solid marrow.  The entire procedure (aspiration and biopsy) usually takes about 30 minutes.
After the samples are taken, a sterile dressing is applied to the site with pressure to stop bleeding.  Once the bleeding has stopped, a new dressing is taped into place.  It is important to keep this dressing dry for 24 hours, as getting it wet can increase the risk of infection.  After 24 hours, you can shower or swim as usual. 
The biopsy site will be sore for at least a few days.  Avoid strenuous activity for a few days.  If you develop an (unusual) fever, severe pain, swelling, redness or drainage from the site, or uncontrolled bleeding, contact your health care provider.  This can indicate an infection.
People ask a lot if the biopsy hurts.  With twilight sedation, it hurt, but not badly, and not for long.  I was pretty sore for about a week after, with a throbbing pain that went down my right leg.  I didn’t have any problems otherwise.    
For people with mast cell disease, there are additional steps and precautions that need to be taken.  When I had mine, I premedicated 12 hours before the procedure, and was then given IV medications an hour before the procedure.  12 hours before, I took 50 mg prednisone, 150 mg ranitidine, 10 mg montelukast and 50 mg diphenhydramine.  One hour before, I received 120 mg methylprednisolone, 40 mg famotidine, and 50 mg diphenhydramine. 
Care must be taken with pain medication for people with mast cell disease.  I received midazolam and fentanyl.  I was advised by my mast cell specialist that I needed to receive twilight sedation for this procedure, as pain is a mast cell trigger, and could cause anaphylaxis for me. 
As always, make sure the medical team is aware of your disease and the procedure if you react/anaphylax/shock.  Always have your Epipens with you.  Never assume that they will have epinephrine in the room.
It is not unusual for multiple biopsies to be needed for diagnosis with SM.  The reason for this is that where the mast cells will cluster in the bone marrow is unpredictable.  Unless you put the needle in the right place, it will be negative.  If you meet three of the minor criteria for SM, you do not need a positive bone marrow biopsy for diagnosis; however, a positive bone marrow biopsy is the most common method of diagnosis.
After the samples are taken, they will be tested for several things.  The samples will be inspected under a microscope to see what types of cells are present and in what quantity, including how many mast cells are present.  There should be some mast cells present, but too many is problematic.  They will also see if they shaped normally, or if they are “spindle shaped,” in which they have pointy edges coming off them (like a star.)  They will use special stains in order to see different cell types, including Giemsa stain for mast cells.
Mast cells in the samples will also be tested for some receptors on their surface, CD117 (encoded by the CKIT gene), CD2 and CD25.  This is done by using special antibodies to these receptors that stick to the receptors, and can then be detected by the operator.  They will also be tested for the D816V mutation in the CKIT gene.  This is done by a testing method called PCR. 
The whole process is not super pleasant, but this test provides answers that are impossible to get otherwise.  And I think you’ll all agree with me that having answers is better than not knowing.