Classifying Symptoms of Hypoglycaemia

Until now the symptoms of hypoglycaemia have been treated as a homogeneous whole. Can these symptoms be divided into different groups?

Hypoglycaemia has effects on more than one part of the body, and the symptoms of hypoglycaemia reflect this. First, the direct effects of a low blood glucose concentration on the brain - especially the cerebral cortex - cause neuroglycopenic symptoms. Second, autonomic symptoms result from activation of parts of the autonomic nervous system. Finally, there may be some non-specific symptoms that are not directly generated by either of these two mechanisms. It is only recently that scientific investigations have taken place to confirm the idea that these separable groups of hypoglycaemic symptoms exist.

As suggested above, there are at least two distinct groups of symptoms during the body's reaction to hypoglycaemia (Hepburn et al., 1991):

• Autonomic, with symptoms such as trembling, anxiety, sweating and warmness.

• Neuroglycopenic, with symptoms such as drowsiness, confusion, tiredness, inability to concentrate and difficulty speaking.

This information can assist with patient education by supplying evidence for separable groups of symptoms, and by indicating which symptoms belong to each group. Some neuroglycopenic symptoms, such as the inability to concentrate, weakness and drowsiness, are among the earliest detectable symptoms, but patients tend to rely more on auto-nomic symptoms when detecting the onset of hypoglycaemia. Paying more attention to the potentially useful, early neuroglycopenic symptoms could help with the early detection of hypoglycaemia.

Similar groups of symptoms of hypoglycaemia have been discovered by asking people to recall the symptoms they typically noticed during hypoglycaemia. However, in addition to the two groups described above, a general feeling of malaise is added (Deary et al., 1993):

• Autonomic: e.g. sweating, palpitations, shaking and hunger.

• Neuroglycopenic: e.g. confusion, drowsiness, odd behaviour, speech difficulty and incoordination.

• General malaise: e.g. headache and nausea.

These 11 symptoms are so reliably reported by people and so clearly separable into these three groups, that they are used as the 'Edinburgh Hypoglycaemia Scale' (Deary et al., 1993). Table 2.2 shows how different researchers have found similar groups of autonomic and hypoglycaemic symptoms.

In addition to the above studies that used patients' self-reported symptoms, physiological studies have also confirmed that the symptoms of hypoglycaemia can be divided into auto-nomic and neuroglycopenic groups. Symptoms such as sweating, hunger, pounding heart, tingling, nervousness and feeling shaky/tremulous (autonomic symptoms) can be reduced or even prevented by drugs that block neurotransmission within the autonomic nervous system (Towler et al., 1993), confirming that these symptoms are caused by the autonomic response to hypoglycaemia. Symptoms such as warmth, weakness, difficulty thinking/confusion,

Table 2.2 Different authors' lists of autonomic and neuroglycopenic symptoms of hypoglycaemia

Autonomic

Neuroglycopenic

Deary et al.

Towler et al.

Weinger et al.

Deary et al.

Towler et al. (1993)

(1993)

(1993)

(1995)

(1993)

Sweating

Sweaty

Sweating

Confusion

Difficulty thinking/

confused

Palpitation

Heart pounding

Pounding heart,

Drowsiness

Tired/drowsy

fast pulse

Shaking

Shaky/tremulous

Trembling

Odd

behaviour

Hunger

Hungry

Speech

Difficulty speaking

difficulty

Tingling

Incoordination

Nervous/anxious

Tense

Weak

Breathing hard

Warm

feeling tired/drowsy, feeling faint, difficulty speaking, dizziness and blurred vision (neuroglycopenic symptoms) are not prevented by drugs that block the autonomic nervous system. Therefore, neuroglycopenic symptoms are not mediated via the autonomic nervous system and are thought to be caused by the direct effect of glucose deprivation on the brain. This type of research has also observed that people tend to rely on autonomic symptoms to detect hypoglycaemia, even when neuroglycopenic symptoms are just as prominent (Towler et al., 1993). Once more, this suggests that more emphasis should be placed on education of the potential importance of neuroglycopenic symptoms for the early warning of hypoglycaemia.

Symptoms might gather into slightly different groupings depending on the situation. The symptom groupings in the Edinburgh Hypoglycaemia Scale were developed from diabetic patients' retrospective reports. However, when people are asked to rate the same group of symptoms during acute, experimentally-induced moderate hypoglycaemia, a slightly different pattern emerges (McCrimmon et al., 2003). In Table 2.3 there is an autonomic grouping, and the single neuroglycopenia group has divided into two symptom groups: one with mostly cognitive symptoms and the other with more general symptoms. This division probably arose because the subjects in the studies used to form Table 2.3 were engaged in cognitive tasks

Table 2.3 Symptom groupings of the Edinburgh Hypoglycaemia Scale during experimentally-induced hypoglycaemia

Neuroglycopenic symptoms

Table 2.3 Symptom groupings of the Edinburgh Hypoglycaemia Scale during experimentally-induced hypoglycaemia

Neuroglycopenic symptoms

Cognitive dysfunction

Neuroglycopenia

Autonomic symptoms

Inability to concentrate

Drowsiness

Sweating

Blurred vision

Tiredness

Trembling

Anxiety

Hunger

Warmness

Confusion

Weakness

Difficulty speaking

Double vision

during the period of hypoglycaemia. Therefore, they would be especially aware of cognitive shortcomings, making this group of symptoms more prominent and coherent.

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