General weakness is not only a subjective feeling of the patient but is also vague enough that it demands seeking clarification by the physician before embarking on its analysis. In this article, Dr. YK Amdekar details on practice concepts that may help physicians decipher the underlying cause.

To read other originals by Dr. YK Amdekar, click here.

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Introduction

General weakness may connote different meanings to different people. When a mother complains about general weakness in her child, it depends on her subjective understanding of what the child has. It may be far from what the real problem may be. Often, a mother equates thin stature of a child to weakness.

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Practice concepts

General weakness is a complaint that mostly does not refer to a neurological disorder. However, one must make sure that weakness does not relate to paresis. Rarely though, severe hypokalemia in a malnourished child or in a sick, elderly individual may present with generalised paresis and so also in case of progressive ascending polyneuritis. So one must confirm that there is no paucity of movements in a child presenting with generalised weakness.

Medically speaking, generalised weakness refers to tired muscles. Muscles are short of desired energy required for movement and so, such a patient wants to move and also can move but finds it very tiring to move.

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What do muscles need for adequate functioning?

Obviously, muscles need oxygen that is provided by the lungs, pumped by the heart and transported through haemoglobin to the required sites. Thus, a child with a slowly developing lung or heart disease or anaemia may fail to deliver adequate oxygen to muscles and so present with generalised weakness. If lung or heart disease or anaemia develops rapidly, the child presents with acute breathlessness rather than generalised weakness. Thus, generalised weakness develops over time and rarely in a short time.

Besides oxygen, muscles need glucose for energy. It is not hypoglycaemia but hyperglycaemia that fails to deliver enough glucose to muscles. If a child is hypoglycaemic, presentation is acute with seizure or change in sensorium. But, in case of hyperglycaemia as in diabetes, muscle cells cannot utilise glucose despite its availability and hence deprive muscles of necessary glucose. Thus, diabetes may present with generalised weakness. A child with diabetes often presents acutely over few days and at times, a phase of generalised weakness is overlooked until the child presents with ketoacidosis and change in sensorium.

Energy comes from calories – though carbohydrates are a major source of calories and a child with severe protein-energy malnutrition (PEM) also has generalised weakness; he/she is reluctant to play and prefers to be inactive. Muscles in such a child are wasted that causes generalised weakness, besides the fact that nutrients are also not available.

Muscles also need intracellular ions such as potassium and magnesium for adequate function. However hypokalemia or hypomagnesemia are mostly acute and so do not present as generalised weakness but manifest as paresis – neurological weakness. Though, rarely renal disease may present with chronic hypokalemia – but primarily it is paresis and not just tired muscles.

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Causes of generalised weakness

As mentioned in the discussion above,

1. Severe PEM is a common cause generalised weakness though major symptoms pertain to acute infection that brings the child to a health facility. In addition, loss of weight and appetite predominate. In older children, PEM is secondary to chronic progressive disease as in case of end-stage renal disease.
2. Generalised weakness may the only presenting symptom in chronic lung diseases such as interstitial lung diseases (chronic bronchitis with emphysema is rare in children), chronic heart conditions (congenital heart defects, rheumatic heart disease and myocardial disorders) and chronic anaemia of various aetiologies (iron or Vitamin B12 deficiency, congenital haemolytic anaemia and marrow aplasia).
3. Diabetes as a cause of generalised weakness should be kept in mind and will be evident only if one asks for polyuria, polydipsia and polyphagia.
4. Generalised weakness is a prominent symptom, other symptoms are often not complained of, unless asked for. Chronic hypokalemia is a rare to present as generalised weakness.

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Clinical approach

History: It is important to confirm that the child can move his/her limbs in all directions, thus ruling out paresis.

Onset and duration: Acute onset within a few days is typical of diabetes that is evident by asking about thirst, increased urine output and increased appetite. Most other conditions present subtly over days or weeks.

Progress: Fast deterioration is a risk if one misses diabetes while other conditions worsen slowly.

Localising symptoms

1. Chronic lung disorders are easily missed as patients get adapted to hypoxia and do not complain about breathlessness though they do have tachypnoea that is not noticed. On direct questioning, one may be able to pick-up slightly fast respiratory rate even at rest.
2. Palpitation may be a symptom in chronic cardiac conditions in older children while the mother may notice precordial hyperactivity in a younger child.
3. Cough may be a minior symptom in both cardiac and lung diseases.
4. Significant pallor is rarely missed by parents and often is a main compliant along with generalised weakness. So it is easy to make out in history itself.

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Physical examination

General appearance

• Tired and chronically-sick look is common to all, except a child with diabetes who may look acutely sick especially if the initial stage is missed
• A child with PEM may be irritable or lethargic depending on severity of protein or calorie deficiency

Growth parameters:

• They are markedly disturbed in PEM but also abnormal in other chronic conditions to a variable extent
• A child with diabetes may have normal growth
• Pallor is striking in case of severe anaemia while many other conditions may also be marginally pale

Heart rate and respiratory rate

They are important to pick up subtle cardiac and respiratory disorders. Mild tachypnoea is easily missed unless one counts respiratory rate over a full minute. If tachypnoea is abnormal as compared to tachycardia, it is likely to be primary respiratory disease while if tachycardia is more abnormal as compared to respiratory rate, it points to cardiac disorder. Such basic signs can pick-up chronic but otherwise silent cardiac or respiratory diseases that are otherwise missed.

Pulse-oximetry

It is now considered as a bedside clinical manoeuvre as much as use of blood pressure in routine clinical practice. This is because it offers great help in early pick-up of respiratory and cardiac conditions. In fact, it is now being used routinely in every newborn for early diagnosis of congenital heart defect.

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Systemic examination

1. Murmur, cardiomegaly, and signs of cardiac failure would suggest a cardiac disease.
2. Mild increase in respiratory rate may be the only finding in chronic interstitial lung disease that is easily overlooked. Pulse-oximetry will show low oxygen saturation in such a case. One must make a habit of noting pulse and respiratory rate judiciously.
3. In case of severe pallor, presence of hepatosplenomegaly suggests haemolytic anemia while absence indicates either deficiency anaemia or marrow aplasia. A child with marrow aplasia looks sick while one with deficiency or haemolytic anaemia is not sick looking.

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Investigations

Specific investigations are planned according to the system involved. However, at times, there is no clue on history or physical examination. In such a case, chest X-ray and echocardiogram/ECG may offer clues. However, if both these tests are normal and one is sure about the problem being pathological, further tests may be necessary to rule out cardiac disease (stress test) and interstitial lung disease (CT scan). Detailed haematological tests can define specific cause of anaemia (serum iron or B12, haemoglobin electrophoresis).

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Management

It would depend on specific diagnosis. What is important to note is the fact that generalised weakness is a vague symptom and cannot be passed on by prescription of a “tonic”. There is a risk of missing life-threatening diseases. A child with PEM needs not only “tonics” but counselling about nutrition and again ruling out comorbid conditions.

In summary, generalised weakness as a presenting complaint needs cautious approach because some of the conditions present with subtle clues on history as well as physical examination that are easily overlooked.

Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.