<<Disclaimer: Verify this information before applying it to your situation.>>
Dr. Horvath was kind enough to put together a reference file answering
some of the recent questions on the diagnostic limitations for celiac
disease.
----
Michael Jones ([log in to unmask]) Orlando, FL USA
One of the Celiac & Cel-Kids Listowners
Limitations in the Diagnosis of Celiac Disease
(A personal opinion - not medical advise)
I understand the existing confusions over the limitations of
intestinal biopsies and serology for the diagnosis of celiac
disease. Before discussing the diagnostic procedures I would like to
give some reasons -in a simplistic way- for the difficulties in the
diagnosis of celiac disease. Based on my experience from seventies
and eighties when I followed the "three-biopsy-rule" for the
diagnosis of celiac disease I concluded that:
-patients with celiac disease have a wide variety of manifestations
from classical symptoms to the asymptomatic cases.
-the individual sensitivity to gluten is very variable from unclear
reasons. The period of gluten challenge resulting in mucosal damage
and the amount of gluten necessary to provoke serological immune
response/histological changes are individually different.
There is no simple explanation for these observations:
- One possibility that patients have the combination of different
"celiac genes". Although we have significant progress in our
knowledge in the molecular genetics of CD, we are still far from a
full understanding. We know the higher frequency of certain genes but
we still do not have a full knowledge.
- The second possible explanation is a difference in the adaptation
of the small intestine. The adaptation means that when a smaller or
larger part of intestine is removed, chronically damaged or
non-functioning the remaining segments are able to compensate the
decrease of absorptive surface. This adaptation process is regulated
by lot of different factors, which include different trophic factors,
hormones and the composition of the diet is also important. To
illustrate the complexity of problem there are lot of different
local intestinal hormones and other known hormones (insulin, thyroid
hormones, steroid hormones) influencing the function and
regeneration of intestine. Certain dietary components such as
glutamine (an amino acid) or fibers also have beneficial effect on
this process.
- There are differences in the local immune response to gluten and
other antigens, toxins and pathogens. The primary function of
intestinal immune system is to protect us from food and bacterial
antigens. If this defense is not functioning well it may result in
an abnormal response and further damage. Alternatively, if it
functions well it will protect from evident damaging factors.
I only mention three main possible components for the
differences we experience in the manifestations of celiac disease.
All of them are discussed in thick textbooks and thousands of
papers.
THE DIAGNOSIS OF CELIAC DISEASE is not simply determined
by a biopsy, but rather based on a combination of:
1. Clinical symptoms
2. Serological testing (and other immunological tests)
3. Intestinal biopsy (histology)
4. Response to a gluten-free diet
In my experience, there are different possible combinations of the
above components, which I will lay out in a table below, with
different cases labeled by the letters A through G (This table is
best viewed in a monospaced font like Courier).
A B C D E F G
Symptoms + + + - - + -
Serology/immunology + ? + + + ? -
Biopsy + + ? + ? ? +
Response to diet + + + + + + +
Although this table can provoke a long scientific discussion,
the main message I am trying to get across is that if somebody has
symptoms or serological/immunological reactions to gluten or abnormal
intestinal mucosa which disappears on a gluten-free diet, this
individual should be considered as gluten sensitive.
I think most of the patients belong to the first group [A].
There is no any difficulty in diagnosing these cases. However, we all
know that the wide diversity of possible symptoms (from mild anemia to
classic celiac appearance) is frequently not appreciated by physicians
practicing in this country.
If somebody has symptoms suggestive of celiac disease, but the
serology is not conclusive [B] and other diseases resulting in
similar symptoms are excluded we should perform intestinal biopsy.
If the biopsy is positive, and the patient has favorable response to
gluten withdrawal the diagnosis of CD is considered proven.
If both the symptoms and serology are suggestive of celiac
disease [C], but the histology is not confirmative a trial with
gluten-free diet should be started. Cases belonging to this group are
reported recently (Picarelli A et al: Gluten sensitive disease with
mild enteropathy. Gastroenterology 1996;111:608-616)
If there are no symptoms but the serology positive (it
frequently happens during screening studies) [D] intestinal biopsy
should be performed. Typical cases are the asymptomatic family
members.
The group [E] is a theoretical possibility. If the serology
positive during a screening test but the biopsy is not conclusive
there are two options. First, to perform sophisticated tissue culture
and immunhistochemical studies on the biopsy specimens to prove
the gluten sensitivity. Alternatively, a trial with a gluten-free diet
and a following the changes in serology titers can be considered.
We may have patients with symptoms suggestive of celiac disease,
who do not have positive serology and the histology is not absolutely
confirmative [F], but other possible causes are ruled out . In these
cases, I believe a trial with a gluten-free diet can be started. I
would like to emphasize here that I do not accept this possibility
without a very thorough medical work-up. Self-diagnosed patients may
have a high risk for other possible harmful conditions (e.g. intestinal
lymphoma).
The group [G] is a theoretical possibility. There are
publications when teenagers undergoing upper GI endoscopy had flat
intestinal mucosa and they responded well to diet. Serological
studies were not reported. They did have recurrent gastric pain,
which was the main indication of endoscopy (Group B?). The intestinal
atrophy was an "accidental" finding. I created this group for
teenagers primarily, because based on my experience this is a "silent
period" of celiac disease. I had a body builder, extremely muscular
boy with flat mucosa and without abnormal serology. He was on diet
temporarily when he was infant and that time responded well to GF
diet.
I would like to emphasize that there are no 100% perfect tests
in the medicine. The diagnosis of every disease requires several
different laboratory and other diagnostic procedures.
THE VALUE OF SEROLOGY TESTS:
In patients without selective IgA deficiency we can accept the
following parameters from the serologic tests:
SENSITIVITY- the proportion of subjects with the disease who have
positive test. It indicates how good a test is at identifying the
disease.
IgA antigliadin antibody test: average: 78% range: 46-100%
IgG antigliadin antibody test: average: 79% range: 57-94%
IgA antiendomysium test: average: 97% range: 89-100%
POSITIVE PREDICTIVE VALUE- is the probability that a person with a
positive results actually has the disease.
IgA antigliadin antibody test: average: 72% range: 45-100%
IgG antigliadin antibody test: average: 57% range: 42-76%
IgA antiendomysium test: average: 92% range: 91-94%
I would like to make two comments:
-patients with selective IgA deficiency are not able to produce IgA
antigliadin and IgA antiendomysium antibodies. Among my pediatric
patients 1 out of 13 patients with CD had selective IgA deficiency
(7.69%). False negatives test results may occur in these patients
-It was clearly shown in large study from Europe (B|rgin-Wollf et al.
Arch Dis Child 1991;66:941-947) that the endomysium antibody (EmA)
test is less specific and sensitive in children below two years of
age. They found that the sensitivity of the EmA test decreased from
98% to 88 % in children younger than 2 years of age. It means that 12%
of their patients with celiac disease, who were younger than two years
of age, but were not selective IgA deficient, did not have increase
in their endomysium antibody levels. Thus, this group is also more
at risk for false negative test results.
VALUE OF INTESTINAL BIOPSY
The intestinal biopsy is an important part of the diagnosis.
However, the routine histological examination has never been
considered as specific itself for celiac disease. There are
sophisticated, but not routinely used tests on biopsy tissues which
can be considered more specific than the simple histological test.
These are computerized morphometric analyzes and specialized
immunological tests on biopsy specimens in the presence of gliadin.
They can be done in cases when there is any doubt regarding the
diagnosis.
The routine histological examination of intestinal biopsy
specimen may be inconclusive in small percentage of patients with
so-called "patchy lesions" in the duodenum. It means that there are
histologically normal looking spots with finger like villi and
pathologic spots showing flattened mucosa in the upper half of the
duodenum. If CD is suspected, the gastroenterologist should obtain
several biopsies from different spots of the whole duodenum. Most of
the endoscopist routinely examine only the upper half of the
duodenum (duodenal bulb and the descending part). The transverse
segment of duodenum is not viewed routinely. Few endoscopic centers
have enteroscope, which is a longer and more flexible endoscope for
the examination of entire duodenum and jejunum. The enteroscopy
allows to obtain biopsies even from the jejunum. The histological
examination of a single biopsy specimen may increases the risk of
false negative diagnosis.
The experience of pathologist in the interpretation of small
intestinal histology is important. In Centers with expertise in
celiac disease, the gastroenterologist routinely reviews the
histologic slides together with the pathologist.
There is still a possibility of inconclusive results if
multiple biopsies are obtained and the histological interpretation
is appropriate (see again: Picarelli A et al: Gluten sensitive disease
with mild enteropathy. Gastroenterology 1996;111:608-616). All disease
has a developmental process. It means that it takes time for the
pathological changes to be evident. There are cases when the symptoms
suggest CD, however, the histology is not conclusive. This problem
occurs in only few of the cases. A repeated biopsy may be necessary
after a period of higher gluten challenge. However, if the
antiendomysium antibody test is positive and the histology is not
conclusive a gluten-free diet is recommended.
Karoly Horvath, M.D., Ph.D.
Associate Professor of Pediatrics
Pediatric Gastroenterology and Nutrition
University of Maryland at Baltimore
|
