Diabetes Mellitus is a metabolic disorder which is believed to be a epidemic across the developing nations usually caused to age groups between 25 to 50. Diabetes Mellitus characterized by chronic hyperglycemia associated with disturbances of carbohydrate, fate and proetin metabolism due to absolute or relative defiency in insulin secreation and/or action. Diabetes causes long term damage, dysfunction and failure of various organs especially the eyes, kidney, nerves, heart and blood vessels. In a nutshell diabetes is appropriately described as a "Metabolic cum vascular disorder". world diabetes day is on 14th November.
Recently the World Health Organization (WHO) in
consultation with an expert committee of the American Diabetes Association
(ADA) has reported a new classification and diagnostic criteria.
The term insulin dependent diabetes mellitus and non-insulin dependent diabetes
mellitus and their acronyms, IDDM and NIDDM are eliminated. These terms have been confusing and have
frequently resulted in classifying the patient based on treatment rather than etiology.
Types of Diabetes Mellitus
(Etiologic Classification of Diabetes Mellitus)
1.
TYPE 1
a)
Autoimmune
b)
Idiopathic
2. TYPE
2
a)
Predominantly
insulin resistance
b)
Predominantly
insulin secretory defects
3. OTHER
SPECIFIC TYPES OF DIABETES
A.
Genetic
defects of beta cell dysfunction, e.g. MODY 1 to 4
B.
Genetic
defects in insulin action, e.g. Type A insulin resistance
C.
Diseases
of Exocrine pancreas, e.g. Fibrocalculus pancreatopathy.
D.
Endocrinopathies,
e.g. acromegaly, cushings etc.,
E.
Drugs-
or chemical –induced, e.g.
glucocorticoids
F.
Infections,
e.g., Congenital rubella.
G.
Uncommon
forms of immune-mediated diabetes, e.g. Stiff Man Syndrome.
H.
Other
Genetic syndromes.
4.
GESTATIONAL DIABETES
(ADA Criteria 2003)
TYPES OF DIABETES MELLITUS:
1.
TYPE 1 DIABETES MELLITUS:
The previously used terminology
is insulin dependent diabetes mellitus (IDDM). These
patients depend on insulin for survival. On withdrawal of insulin they go into
hyperglycemia, ketoacidosis and coma.
Type 1 diabetes has its onset most often in childhood and adolescence,
although it may occur at any age. Though usually abrupt in onset, it can be
protracted in its course (slow onset IDDM, LADA – Late onset Autoimmune
Diabetes of Adult). The genetic factors, autoimmunity and environmental factors
play a role in the causation and precipitating type 1 diabetes
Type 1 diabetes is recognized to be due to autoimmune
destruction of b
cells. Type 1A immune mediated is characterized by the presence of islet cell,
GAD (Glutamic acid decarboxylase), IA-2, IA-2B or insulin autoantibodies that
identify the autoimmune process that leads to b cell destruction, in some
subjects no evidence of autoimmunity is present; these cases are classified as
Type 1B (idiopathic). Type 1A diabetics are prone to other autoimmune disorders
such as Grave’s disease, thyroiditis,
autoimmune addison’s disease, ovarian failure, vitiligo, pernicious anemia etc
.
There
is a strong positive genetic association of type 1 diabetes with HLA -B8- DR
and/or DR4. Recent research has shown that there is increased susceptibility to
type 1 DM when the amino acid Asp 57 is absent in DQ B with the presence of Arg
52 in DQ A.
The absence or very poor response of glucogon
stimulated `C` peptide levels are
diagnostic of type 1 diabetes as these patients have very low residual beta
cell function (b cell
reserve <10%).
2.
TYPE 2 DIABETES MELLITUS:
The previously used terminology
is non-insulin dependent diabetes mellitus (NIDDM). Type 2
diabetes usually begins in the middle age or after 40 years. It is not uncommon
to come across the development of diabetes in third decade itself in our
country. The
pathophysiological basis is a combination of impaired beta cell function, with
marked increase in peripheral insulin resistance at receptor /post receptor
levels and increased hepatic glucose output production. Their circulatory
levels of insulin and C-peptide may be variable ranging from hyper to normo
insulinemic levels in a majority of the subjects. Type 2 diabetes is further
sub-classified into obese and non-obese types.
Coma
is rare in type 2 diabetes, but may result from extreme hyperglycemia and
hyperosmolarity; ketoacidosis can occur in fulminating illnesses due to acute
increase in insulin requirements but "spontaneous"
ketosis does not occur. Lactic acidosis
is rare.
Given all credence to the latest
classification based on etiology; for practical purposes, the classification of
type 1 and type 2 diabetes for a clinician is mostly clinical with a key feature being
proneness to ketosis and dependence on insulin. It also includes other clinical
aspects like age and onset, family history of diabetes or autoimmune disease
and presence or absence of obesity.
GESTATIONAL DIABETES MELLITUS
(GDM):
Gestational
diabetes mellitus is defined as glucose intolerance developing or recognized
during pregnancy. In the post partum period they may revert back to normal,
continue to have impaired glucose tolerance, or develop frank diabetes after a
few years. Hence patients with GDM must undergo OGTT with 75 gm glucose six
weeks after delivery for reclassification of their diabetic status and repeated
after six months.
Gestational diabetes mellitus merits separate
consideration by virtue of increased fetal risk associated with it and
likelihood of developing diabetes in the future (Ref. Chapter on pregnancy
& Diabetes).
STAGES OF DIABETES:
Stages of diabetes range from normal glucose tolerance,
through IGT, and IFG (impaired fasting glucose), into frank diabetes mellitus,
which may be non-insulin requiring, insulin requiring for control and insulin
requiring for survival. Type 1 DM can be found across the whole spectrum. In
the early stages of treatment there can be a period of non-insulin requirement,
but later followed by insulin requirement for survival. In type 2 DM, insulin
may be required during a period of ketoacidosis precipitated by severe stress
or infection.
In an overweight type 2 DM patient, weight loss and
physical activity and weight loss will result in normal glucose tolerance. This
does not indicate cure and the person still has type 2 DM.
DIAGNOSIS OF DIABETES MELLITUS:
Diagnosis of diabetes mellitus based on urine
sugar is unreliable. When the fasting plasma glucose is above 126mg% or random
blood glucose more than 200-mg%, on more than one occasion the diagnosis of
diabetes can safely be made. When in
doubt, to diagnose diabetes mellitus, a standard glucose tolerance test is
used. The WHO recommends specific test procedure and the criteria for the
diagnosis of diabetes
ORAL GLUCOSE TOLERANCE TEST
(OGTT):
The
OGTT is recommended for diagnosis/ exclusion of diabetes and is the only test
for IGT. The use of glycosuria (urinary glucose) as a diagnostic criterion for
diabetes is obsolete and at the best warrants further investigation.
The
OGTT is done in the morning after 10 - 16 hours of overnight fast (water may be
taken) following at least three days of unrestricted diet (more than 150 gm of
carbohydrates) to sensitize the beta cells of pancreas. During the test only
water is drunk to alleviate the thirst. Smoking and all physical activity
should be avoided.
TEST: A
fasting blood sample should be taken before giving glucose load. The subject
then drinks 75 gms. of glucose in 250 - 300 ml of water. Children should receive glucose load at 1.75
gm/kg body weight to a maximum of 75 gms. (The glucose load should be consumed
over a period of five min). A further blood sample must be collected 2 hours
after the load. The criteria for interpretation of OGTT are he same regardless
of the age of the subject. Blood samples must be collected into fluoride-
oxalate tubes, which prevent the red cells from metabolizing glucose. The
laboratory values in mentioned below table
Diagnostic Values For Oral Glucose Tolerance Test (OGTT) For Diabetes Mellitus
Whole blood
glucose
Plasma glucose
----------------------------------------------------------------------------------
Venous Capillary Venous Capillary
DIABETES
MELLITUS:
Fasting
values >
6.1 (>110) > 6.1 (>110) > 7.0 (>126) > 7.0 (>126)
2
hr. after 75 gm
glucose
load > 10.0 (>180) >11.1( >200) >11.1
(> 200) >12.2 (
>220)
