Mast Cells and Myelofibrosis
W A L T E R C. U D O J I , M.D.,
AND S. A L I RAZAVI,
M.D.
Department of Pathology, University of Cincinnati Medical Center, 234 Goodman Street, Cincinnati, Ohio 45229
ABSTRACT
Udoji, Walter C , and Razavi, S. Ali: Mast cells and myelofibrosis. Am J Clin
Pathol 63: 203-209, 1975. Autopsy of a patient with well-documented
myelofibrosis revealed marked proliferation of mast cells associated with
areas of bone-marrow and splenic fibrosis. The findings suggest that the
local fibrosis represents the healed phase of an inflammatory reaction
mediated by mast cells via the release of histamine into the tissue spaces.
Tissue mastocytosis may be the pathogenetic mechanism in some cases of
myelofibrosis. (Key words: Mast cells; Injury; Degranulation; Histamine
release; Inflammation; Healing; Myelofibrosis.)
THE MAST CELLS were first recognized
and described by Ehrlich, 8 and since then
many functions have been assigned to
them, including formation of histamine, 7
heparin, 3 and hyaluronic acid. Under
normal conditions mast cells are absent
from the peripheral blood, and they are
rarely seen in bone marrow. 8 On the
other hand, systemic dissemination and
formation of tumorous aggregates by
these cells are known to occur in such
diseases as urticaria pigmentosa and
mast-cell leukemia. This report describes
the lesions seen in a patient in whom
myelofibrosis was associated with a great
increase in mast cell population but without a leukemic phase.
Report of a Case
A 73-year-old Caucasian man had been
known to have hypertension and cardiomegaly since 1968. He had been
treated in different clinics for hypertenReceived May 17, 1974, received revised manuscript July 29, 1974; accepted for publication July
29, 1974.
Address reprint requests to Dr. Udoji, Department of Pathology, University of Cincinnati Medical
Center, 234 Goodman Street, Cincinnati, Ohio
45229.
203
sion (blood pressures ranging from
140/90 to 150/85 mm. Hg) and for congestive heart failure with small doses of
digoxin and diuretics. In August 1970, he
had complained of lethargy; a chest x-ray
at that time showed a few densities in the
ribs. They were suspected to be metastases, but a primary tumor was not detected. He continued to receive digoxin
and diuretics. Clinically, he was also considered to have moderate aortic stenosis
and arteriosclerotic heart disease.
In J u n e 1972, the patient was seen
because of weakness, anorexia, and pains
in the back, right hip, and shoulders. A
diagnosis of myelofibrosis was made on
the basis of an iliac bone biopsy and x-ray
of the skeletal system. The roentgenographic findings consisted of diffuse
myelosclerosis involving the entire skeletal
system and were most severe in the spine,
ribs, and upper femora. A subsequent
review of the bone biopsy suggested a
diffuse mast-cell disease, but the patient
refused further investigation.
During the period of treatment for
heart failure there were episodes of cerebral and anterior myocardial infarction,
but the patient remained free of symp-
204
UDOJI AND RAZAVI
toms of mast-cell disease such as flushing and diarrhea. He did not have
asthmatic attacks or a history of chronic
infection, exposure to toxic agents, or
exposure to radiation. No drug was given
for the mastocytosis. The cardiac failure
worsened and the patient died at home
from bronchopneumonia and cerebral infarction.
Laboratory Findings
June 1972. Hemoglobin 13.9 Gm. per
100 ml.; hematocrit 45%; erythrocyte
count 4.7 million per cu. mm.; leukocyte
count 8,200 per cu. mm., polymorphonuclears 6 1 % , stabs 3%, lymphocytes
32%, monocytes 4%.
March 1973. Hemoglobin 13.3 Gm. per
100 ml.; hematocrit 40%; erythrocyte
count 4.5 million per cu. mm.; leukocyte
count 6,600 per cu. mm., polymorphonuclears 49%, lymphocytes 4 1 % ,
monocytes 10%.
August 1973. Hemoglobin 14 Gm. per
100 ml.; hematocrit 39%; leukocyte count
6,900 per cu. mm., polymorphonuclears
44%, stabs 4%, lymphocytes 28%, monocytes 24%.
T h e peripheral blood smears were described as normocytic and normochromic
with occasional target cells. Tear-drop
erythrocytes and mast cells were absent.
Serum cholesterol, triglycerides, and clotting profiles were normal. Alkaline phosphatase was 180, 170 mU. per ml. by
SMA 12/60; fasting blood glucose 90 mg.
per 100 ml., blood urea nitrogen 7 mg.
per 100 ml. In August 1972, serum
histamine was 3 fig. per 100 ml. (normal
5 - 1 5 fig. per 100 ml.) and the 24-hour
urinary histamine was 86 fig. per 100 ml.
(normal 15-80 fig. per 100 ml.).
Autopsy Findings
Cardiomegaly (450 mg.), calcified aortic
valve cusps, and arteriosclerosis of the
aorta, coronary and carotid arteries were
A.J.C.P.—Vol.
63
found. There was fibrosis of the marrow
of cervical, thoracic and lumbar vertebrae
and the ribs. The spleen weighed 320
Gm. and was firm but without any obvious
infiltrates.
Method
Tissues were obtained and studied at
the time of necropsy, then fixed in neutral
buffered formalin and stained with
hematoxylin and eosin and with Giemsa
stain. In addition, the bone marrow was
fixed in Zenker's solution and stained with
1% toluidine blue; this provided the best
method for demonstrating the metachromasia of mast cell granules.
For electron microscopy, the tissues
were fixed in 4% glutaraldehyde, transferred to cacodylate buffer, and postfixed
in 1% buffered osmic acid. They were
embedded in Epon, stained with uranyl
acetate and lead nitrate for 30 minutes,
and examined in a Siemens 101 microscope at 80 KV.
Results
The main findings were in the bone
marrow and spleen, although the latter
was involved to a lesser extent than the
former. Splenomegaly was not prominent; anemia, extramedullary hematopoiesis, and the skin lesions of urticaria pigmentosa were absent. Other negative findings were the lack of mast
cell infiltrates in toluidine blue- and
Giemsa-stained sections of the skin, heart,
aortic valve, aorta, lung, brain, liver, intestines, and lymph nodes.
T h e splenic follicles were reduced in
size, and there were patchy areas of
recent fibrosis in which small collections
of mast cells were identified with Giemsa
stain. T h e fibrosis of the bone marrow was
generalized and finely textured (Fig. 1), in
various stages of development, and was
sometimes very dense around small capillaries (Fig. 2). In the vicinity of these
February 1975
MAST CELLS AND MYELOFIBROSIS
205
FIG. 1 (upper). Myelofibrosis. A mixture of mast cells and marrow cells is present between the strands of
fibrous tissue. Bone marrow. Hematoxylin and eosin. x 110.
FIG. 2 (lower). Well-developed focus of fibrosis within marrow cavity. Giemsa stain, x 110.
206
A.J.C.P.—Vol. 63
UDOJI AND RAZAVI
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MAST CELLS AND MYELOFIBROSIS
February 1975
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FIG. 5. Nodule of mast cells in bone marrow. More than 50% of the nucleated
cells are mast cells. Toluidine blue. x265.
vessels, the early fibrotic lesions consisted
of concentric perivascular cellular whorls
formed mainly by compressed and elongated mast cells. Some mast cells and their
granules were demonstrated within these
foci by the Giemsa stain (Figs. 3, 4), but
the purple-red metachromasia of the
granules was easily displayed with toluidine blue.
The nonfibrotic areas of the bone marrow showed hyperplasia of the myeloid
series mixed with many mast cells (Fig. 5).
The mast cells were 15-20 /xm. in diameter; they had irregular outlines and single
round nuclei with dense chromatin. T h e
quantities of granules in individual cells
varied, and there was moderate nuclear
and cellular pleomorphism, indicating
that cells in different stages of development were present. They were concen-
trated around blood vessels, at the advancing margins of the fibrotic zones, and
in the interstices of the recently formed
connective tissue.
By electron microscopy, the mast cells
have an irregular shape, but no surface
projections. Apart from a few areas of
rough endoplasmic reticulum, the cytoplasm was filled with round or oval
granules bound by double membranes
(Fig. 6). T h e granules that did not have
internal structures were 0.25-1 /i.m. in
diameter and of two types—the light
and the dense granules. Both kinds of
granules could be found in the same cell,
but only the former type was seen in the
mast cells surrounding the fibrotic areas.
These light granules are thought to represent those that have discharged their
contents.
208
UDOJI AND RAZAVI
A.J.C.P.—Vol. 63
FIG. 6. Electron micrograph of a mast cell in connective tissue (ct). The cytoplasm contains many light granules,
(g) and little endoplasmic reticulum (r). N = nucleus. Uranyl acetate and lead nitrate, x 16,800.
Inset: Some of the dense granules seen in another mast cell. Bone marrow. X 61,400
Comments
A survey of various tissues obtained at
autopsy indicates mast cells are present
only within and around the areas of
myelofibrosis.
A great amount of the knowledge of
mast cell morphology and function has
been derived from studies in experimental animals.3>7,16 Their location around
blood vessels is well known, and this may
partly account for the perivascular distribution of lesions in the bone marrow.
Platelets and mast cells contain most of
the histamine in the body. 13,14 Physical
and chemical injuries, such as those produced by irradiation or pharmacologic
agents, can cause degranulation of mast
cells with release of histamine. 7,12 ' 18 In
addition to these types of injuries, mast
cell granules can also be released by less
commonly encountered types, one of
which is anaphylactic injury. 10 Liberated
histamine is capable of inducing tissue
responses characteristic of acute inflammation. 9 Whether the histamine acts
as a mediator in the inflammatory reaction to tissue injury has been debated
for some time, but there is strong evidence that mast cells have such a role, 16,17
and also function in the basic process of
wound healing, and possibly in immunoallergic reaction. 1
There is a correlation between the
quantity of histamine and hyaluronic acid
(ground substance) of various tissues and
their mast cell content. 13 A single deter-
February
1975
MAST CELLS AND MYELOFIBROSIS
mination of serum histamine was normal,
while the 24-hour urinary value was
slightly high. Since elevations of blood
histamine may be short-lived, the urinary
value is considered to be proportional to
circulating histamine. 5 Besides, the urinary level is subject to rebound depression following a large urinary output. 4,5
Perhaps histamine production and circulation were increased in the patient despite the lack of symptoms usually attributed to hyperhistaminemia.
Although the association of mastocytosis with fibrosis is known, 15,19 the
presence of mast cells in fibrotic areas
does not necessarily signify a cause-andeffect relationship, but the morphologic
correlation is so striking in this case as to
suggest that the fibrosis had been initiated
or promoted by mast cells in these tissues
by way of an acute inflammation, and that
mast cell proliferation represents a usual
response to some types of injury in an
organ. In this regard, it is of interest that
Rebuck 11 has shown that mast cells and
basophils of man react to a variety of
inflammatory stimuli by increases in
numbers. Asboe-Hansen 2 has reported
that the formation of new connective
tissue requires some activity of mast cells,
and that the mast cells increase in number
as healing progresses. That the myeloid
lesions are present in different stages of
development also suggests that the injury,
whether physical, chemical, or immunoallergic in nature, occurred separately and
repeatedly, with the release of an inflammatory mediator on each occasion. The
marrow fibrosis is thus the end stage of
this repeated injury.
It is suggested that in this case and in
others, myelofibrosis may result from
localized inflammation and repair that
occur in the mesenchymal tissue of reticuloendothelial organs.
209
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