Tireoidite linfocítica - Repositório Aberto da Universidade do Porto

characteristics of the thyroid cells
constitutes one of the most remarka­
ble morphological aspects of the
lymphocytic thyroiditis.
- Some morphological and immunocy-
tochemical characteristics point
to a functional alteration of the thyroid
cells.
- "Growing nodules" are frequently
found in lymphocytic thyroiditis but
in most cases these are very small.
The tendency to nodularity results
mainly from the convergence of two
factors: functional alteration of the
thyroid cells and increased stimulation
usually by TSH.
- The lymphoid infiltrate is composed
of T cells, namely helper T lympho­
cytes and supressor T lymphocytes,
and B cells capable of producing
immunoglobulins. Its pattern is of
the "reactive type".
- A considerable increase in fibrous
tissue can only be found in some
cases of lymphocytic thyroiditis.
It is suggested that it may be secondary
to autoimmune processes directed
against components of the intersticial
matrix or that it results from an
unbalance between synthesis and
reabsortion of the components of
the intersticial matrix.
- "Depositis" of immune complex type
situated by the epithelial thyroid
basal lamina are rather frequent
but are not exclusive of lymphocytic
thyroiditis, as they can also be seen
in cases of diffuse hyperplasia (Graves'
disease).
At the conceptual and pathogenic level:
- The distinction between focal and
diffuse forms of lymphocytic thyroiditis
is based on the abundance of the
lymphoid infiltrate; the criteria in
which this distinction is established
are arbitrary.
- Focal lymphocytic thyroiditis should
not therefore be considered as an
early stage of diffuse lymphocytic
thyroiditis, although one can not
exclude the possibility of seeing some
cases developing into diffuse situation.
- Focal lymphocytic thyroiditis and
diffuse lymphocytic thyroiditis are
regarded as morphological expressions
from one and the same autoimmune
situation.
- The entity lymphocytic thyroiditis
is defined by clinical, immunological
and morphological parameters and
corresponds to one of the several
conditions designated as autoimmune
thyroid disease.
- This autoimmune thyroid disease
results from a disfunction of the
immune system which probably reflects
a decrease in the regulatory activity
carried out by specific suppressor
T lymphocytes.
- The derangement of the immune
system has a genetic basis not yet
clarified, but it may be related to
the major histocompatibility complex.
- The immune response is also influen­
ced by genes which interfere in the
regulation of the immunoglobulin
synthesis.
- The disfunction of the immune system
allows the production of anti-thyroid
antibodies, namely to thyroglobulin,
microsomal antigens and TSH receptors.
- The anti-TSH receptor antibodies
may be considered as stimulator
or inhibitor respectively of the function
and/or the cellular growth. These
auto-antibodies are particularly im­
portant in Graves' disease (predomi­
nance of the stimulating effect of
the auto-antibodies) and in primary
myxedema (predominance of the
blocking auto-antibodies).
- In lymphocytic thyroiditis there are
still other genetically determined
alterations: functional alterations,
namely related to the iodine metabo-
108