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8.
Instrumental diagnosis of primary hyperthyroidism
The
recourse to imaging in IPTp diagnostics enables the identification of
one or more sources of parathormone hyperincretion, by recognising its
exact location and its volumetric and morpho-structural features.
This
investigation is not aimed at making a diagnosis, which falls within
the specific competence of the clinician or of the laboratory technician,
but at providing a guideline for possible therapeutic procedures aimed
at the ablation of the affected gland or glands.
The
localization of parathyroid glands by means of imaging methods is supposed
to allow identification of the nodule (visualisation) and accurate identification
of its origin (typing).
The
main problem the imaging diagnostician is faced with is represented
by the volumetric exiguity of the parathyroid glands, not only under
normal but also under pathological conditions, as well as by their oblong,
and often ribbon-like, morphology, which make them difficult to locate
by means of the various visualisation techniques available. Parathyroid
glands need to be distingui-shed from possible thyroid nodules, lymph
nodes and neurinomas.
Some-times
it is even difficult to distinguish them from certain muscular structures
of the neck.
These
problems are solved in part by means of medico-nuclear methods, which
are not only based on the size but also on the metabolic activity of
the parathyroid tissue. Picture 7 supplies the clinician with a practical
route to be followed in the event of pre-surgery localisation of IPTp
forms.
9.
Secondary and tertiary hyper-parathyroidism IPTs is an acquired disorder
which is indicative of parathyroid hyperfunction in response to the
perturbation of one or more levels of the feedback systems controlling
PTH secretion and synthesis. It is more common in the event of kidney
diseases, but it is also present in other vitamin D deficiency or vitamin
D resistance conditions.
IPTs
still represents today the most common bone disease in uremic patients.
The term "renal osteodystro-phia" groups various histologic pictures:
osteopathia related to secondary hyperparathyroidism (IPTs) or osteitis
fibrosa
-
a high-turnover form
-
osteo-malacia and dynamic osteopathia
-
low-turnover forms - mixed osteopathia (mixed histologic reports hinting
at osteitis fibrosa and osteomalacia) and osteopathia related to osteoarticular
deposits of beta 2 microglobulin.
In
IPTs-related osteopathia the increase in PTH serum levels associated
with hyperplasia of the parathyroid glands, is the constant and basic
factor displayed very early in chronic renal insufficiency (IRC), when
the glomerular filtrate drops below 80 ml/min.
The
two major inhibitors of PTH synthesis and secretion are ionised calcium
calcitriol, and these are both reduced in IRC. IPTs is also present
in nutritional, gastrointestinal and empathic disorders. In fact, vitamin
D requires bile salts for an adequate intestinal absorption and its
absorption is reduced in conditions accompanying steatorrhea.
The
preser-vation of a normal calcium homeostatis therefore requires an
adequate dietary supply of calcium, phosphorus and vitamin D, their
adequate intestinal absorption and an adequate vitamin D metabolism.
When,
for any reason, one of these conditions is not complied with, a relative
hypocalcemia results. Since the parathyroid glands are extra-ordinarily
sensitive to minimum changes in circulating ionised calcium, this activates
the secretion of PTH, which will in turn stimulate the production of
1,25(OH)2D3, if the empathic conditions (substrate availability) or
the kidney conditions will allow it.
Examples
of possible causes of inhibition of one or more stages of this homeostatic
system are an insufficient intake of dairy products, digestive deficiencies
(owing to pancreatic or biliary insufficiency), radical gastroenteric
surgery, alterations of hepatic metabolism and their conse-quen-ces
on vitamin D activation process, etc.
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