Clinical presentation of diabetes mellitus
The body appears unable to sense glucose levels directly, but people with diabetes learn to appreciate when their blood glucose is outside the normal range by indirect cues, such as thirst when the glucose is too high and sweating and palpitations when it is too low. Diabetes may present acutely, with the three classic symptoms of thirst, polyuria and weight loss; even so, clinical recognition may be delayed until the patient is seriously ill. Many forms of diabetes, including type 2, present less dramatically. Increased thirst and polyuria may not be noticed because they develop slowly, and weight loss may be welcomed by those who are trying to diet. People at this stage of diabetes may call on their doctor with a range of non-specific symptoms such as tiredness and loss of energy; alternatively they may come to notice because of acute complications of diabetes, including hyperglycaemia emergencies and infections, or longer term complications including retinopathy, neuropathy, cataracts, cardiovascular or cerebrovascular disease. People with type 2 diabetes may have had the condition for several years before they come to clinical notice, and many countries now have screening policies to allow earlier detection and treatment.
Early recognition of diabetes is important, not least because delayed recognition may result in hospital admission with a metabolic emergency. Delayed recognition of type 2 diabetes may mean that avoidable long term complications of diabetessuch as retinopathyor neuropathyare already present at diagnosis.
The classic symptoms of diabetes form the triad of thirst, polyuria and weight loss:
Thirst arises as a consequence of dehydration resulting from loss of fluid, salt and other electrolytes in the urine. The acute thirst of type 1 diabetes may be almost unquenchable. Some attempt to slake their thirst with sugar-containing fluids such as Coca-Cola, thus creating a spiral of hyperglycaemia, dehydration and increased craving for fluids.
Polyuria develops when the rate at which glucose enters the proximal tubules of the kidney exceeds the capacity of the tubules to pump glucose back into the circulation. This is achieved by an active transport system which (in most people) can extract almost all glucose below a concentration of ~10 mmol/l (180 mg/dl). Above this point, known as the renal threshold for glucose, glucose spills over into the urine. This exerts an osmotic effect, causing loss of water, salt and other electrolytes from the body, and resulting in dehydration and thirst.
Weight loss is a consequence of calories lost as glucose in the urine, amounting to hundreds of grams of glucose per day in severely uncontrolled diabetes. This is aggravated by insulin deficiency, which accelerates glucose production by the liver while promoting breakdown of fat and protein; the glucose loss and metabolic inefficiency of uncontrolled diabetes thus produces a state of accelerated catabolism.
Although most people with clinical diabetes will have experienced the classic symptoms described above, these may not be mentioned spontaneously, especially when they have developed slowly and over a long period of time. When this is the case, diabetes may come to attention in many other ways.
Tiredness and lack of energy are common symptoms, but not at all specific for diabetes. Changing glucose levels can produce osmotic changes in the lens of the eye, causing changes in visual accommodation resulting in visual blurring, and many freshly diagnosed patients have a new pair of glasses which (unfortunately) will no longer be right for them once the glucose abnormality has been corrected! Another common presentation is with pruritus vulvae (genital itching) in women or balanitis (inflammation of the prepuce) in men. This is due to Candida albicans, a fungal infection which grows more readily in the presence of glucose.
Other presentations represent early complications of diabetes, including characteristic retinal changes spotted by an optician, cataracts, or peripheral neuropathy presenting with numbness and tingling in the feet. Others again come to notice with arterial insufficiency affecting the heart, cerebral vessels or peripheral circulation.
Finally, patients may present late with the metabolic emergencies of diabetic ketoacidosis, typical of type 1 diabetes, or the hyperosmolar non-ketotic state resulting from uncontrolled type 2 diabetes. Other associated emergencies are infections of the foot, skin infections (often staphylococcal), systemic infections (sometimes atypical) or abscesses.
The presentation of diabetes varies with age:
Presentation of Diabetes in Children
Children with type 1 diabetes mellitus may have intermittent symptoms for many months before diabetes is recognised, with a typical interval of 4-6 weeks before diagnosis. In previous years a third or more of children presented in diabetic ketoacidosis, but this proportion has fallen markedly with greater awareness of the condition. The importance of early recognition is shown in the observation that children with an affected family member rarely present as an emergency.
Younger children present more of a diagnostic challenge because they are less able to articulate their symptoms, and may come to medical attention because of failure to thrive or bed-wetting; a higher proportion of young children will end in hospital because of later presentation.
Children with classic type 1 diabetes require immediate treatment with insulin. In contrast, children with MODY or early onset type 2 diabetes may have few symptoms at diagnosis. MODY may be recognised because of a strong family history of diabetes, whereas children with type 2 diabetes are typically overweight.
Physicians should note that overweight adolescents who appear to have type 2 diabetes may in fact have autoimmune diabetes and be at risk of developing ketoacidosis. Some people refer to this mixed form as "double diabetes".
Presentation in Adult Life
Type 1 diabetes may develop at any age, but in Western societies is more common than type 2 diabetes under the age of 30. Type 2 diabetes mellituspresents earlier in those who are overweight and in susceptible ethnic populations.
Both types of diabetes may present in similar ways, and the distinction between them is not always straightforward. Leanness, acute onset, ketonuria and/or ketoacidosis point to type 1 diabetes, and overweight, slower onset, absence of ketonuria and markers of increased susceptibility (previous gestational diabetes, family history, ethnicity) suggest type 2 diabetes. Other possible causes (see
Other types of diabetes mellitus) should always be considered.
The average age of diagnosis of type 2 diabetes is in the early 60s, and diabetes is often (but not always) accompanied by other features such as overweight, abdominal fat distribution, hypertension and hyperlipidaemia (see The type 2 syndrome). Absence of these features may suggest late onset type 1 diabetes or LADA- Latent Autoimmune Diabetes of the Adult.
Diabetes in Later Life
Hyperglycaemia may cause fewer symptoms in older people. The likely reason for this is that the renal threshold for glucose rises with age and declining renal function, so that osmotic symptoms caused by glucose loss in the urine are less prominent. Old people may also have reduced appreciation of thirst. This, combined with renal insufficiency, leaves them at risk of dehydration, especially when the renal threshold is exceeded.
Diabetes at every age has the potential to precipitate a metabolic emergency, and type 1 diabetes can and does present with ketoacidosis in very old people. There is therefore no such thing as "mild diabetes".
This having been said, glucose tolerance deteriorates with age, and many elderly people experience borderline levels of hyperglycaemia with few symptoms or none. Careful surveillance is necessary, but quality of life should take precedence over long-term prognosis, which is anyway little affected in this situation.