Scientific Foundations of Biochemistry in Clinical Practice

David L. Williams,Vincent Marks

• Editorial: Butterworth-Heinemann
• Año: 2014
• ISBN:
  9781483193625
• Edición: 2
• Categoría: Biological Sciences
• Categoría: Biophysics

Scientific Foundations of Biochemistry in Clinical Practice, Second Edition describes the pathological aspects of general metabolic disorders. This book is organized into 10 sections encompassing 45 chapters that discuss the nature of disorders involving disturbance in hydrogen ion concentration and blood gases, as well as the disorders of fluid and electrolyte balance. Some of the topics covered in the book are the chemical analysis of urine; neonatal screening for biochemical disorders; clinical biochemistry of alcohol, in intensive and postoperative care; psychiatric disorders of biochemical origin; abnormalities of the plasma proteins; assessment of gastrointestinal function; and calcium metabolism. Other chapters examine the nature, conditions, and diagnosis of bone disorders. A chapter emphasizes the functions of hypothalamus and pituitary. Another chapter looks into the biochemistry and toxicology of metals. The final chapters are devoted to the classification of connective tissue diseases and to the examination of clinical biochemistry of the central nervous system. The book can provide useful information to doctors, biochemists, students, and researchers.

SECTION 1

GENERAL METABOLIC DISORDERS

Outline

Chapter 1: Nutritional Disorders

Chapter 2: Obesity

Chapter 3: Disorders Involving Disturbances in Hydrogen Ion Concentration and Blood Gases

Chapter 4: Disorders of Fluid and Electrolyte Balance

Chapter 5: Polyuria and Disorders of Thirst

Chapter 6: Diabetes Mellitus

Chapter 7: The Clinical Biochemistry of Alcohol

Chapter 8: Psychiatric Disorders of Biochemical Origin

Chapter 9: The Clinical Biochemistry of Neoplasia

1

Nutritional Disorders

J.W.T. Dickerson

Publisher Summary

This chapter presents an overview of nutritional disorders. Protein-energy malnutrition (PEM) represents a breakdown of adaptive mechanisms, which is manifested as clinical illness. PEM is characteristically a disorder of children and as such is the most widespread and serious nutritional problem known to medical science. The chapter discusses the difference between marasmus and kwashiorkor. In marasmus, the child is underweight with very little body fat and consequent loosening of the skin. There is also muscle atrophy and, depending on the chronicity of the condition, short stature. Kwashiorkor, on the other hand, is characterized by skin and hair changes, edema, “moon face,” fatty liver, hypoalbuminaemia, and psychomotor changes. The clinical manifestations of this disease differ in different parts of the world as also does the age of development. Edema is the cardinal feature of kwashiorkor. The severity differs widely from one child to another and may manifest itself by puffiness around the eyes and swelling of the feet and hands or in other cases, it may be more generalized. The accumulation of fluid in the extremities may mean that severe dehydration may be present in a child with edematous legs.

Protein–energy malnutrition

Introduction

Protein–energy malnutrition in children

Vitamin deficiency and excess

Introduction

Clinical features

Assessment of vitamin status

Trace element deficiency and excess

Introduction

Clinical features

Determination of trace element status

Conclusions

PROTEIN–ENERGY MALNUTRITION

Introduction

The human body possesses considerable powers of adaptation to changes in its environment and this is nowhere more marked than in response to a decrease in nutrient availability. It is clear then that we cannot suppose that there is only one ‘normal’ nutritional state of the organism, and adaptation over a wide range of nutrient availability is compatible with health. Protein-energy malnutrition (PEM) represents a breakdown of adaptive mechanisms, which is manifested as clinical illness.¹ PEM is characteristically a disorder of children and as such is the most widespread and serious nutritional problem known to medical science. As we shall see, the causes are complex, with a large number of interacting factors, but the basic cause is lack of sufficient food of the right kind. PEM may, however, occur as a secondary consequence of other diseases that interfere with the ingestion of food or the absorption of nutrients, or in which there are losses by abnormal routes (i.e. fistulae) (see Ch. 12). The most severe form of malnutrition in adults is that which occurs in patients with cancer and is known as cancer cachexia (see Ch. 9). Disorders associated with obesity are discussed in the next chapter.

Protein–energy Malnutrition in Children

Classification

PEM is a term coined originally as ‘protein-calorie malnutrition’ to cover a spectrum of conditions ranging from marasmus at one extreme to kwashiorkor at the other. The term ‘marasmus’ is derived from the Greek marasmos meaning wasting and has been recognized for centuries as being, with gastroenteritis, a major cause of infant mortality. The term ‘kwashiorkor’ was first used by Dr Cicely Williams in 1933 to describe a condition that she recognized in the then Gold Coast. The word is taken from the Ga language of Ghana and literally means ‘the disease the first child gets when the second is on the way’.

In marasmus the child is underweight with very little body fat and consequent loosening of the skin. There is also muscle atrophy and, depending on the chronicity of the condition, short stature. Kwashiorkor, on the other hand, is characterized by skin and hair changes, oedema, ‘moon face’, fatty liver, hypoalbuminaemia and psychomotor changes. The clinical manifestations of this disease differ in different parts of the world, as also does the age of development. These differences have tended to lead to some confusion in nomenclature and classification of the different forms of PEM.

A classification of PEM should be suitable for use in:

1. The international classification of diseases

2. Prevalence studies and other observations in communities

3. Clinical and research investigations.

The simplest classification is that known as the Wellcome classification (Table 1.1), which is based simply on the deficit in body weight and the presence of oedema. This classification has advantages because of its simplicity, but it cannot be applied when the age of the patient is not known and does not take into account the chronicity of the disease process.

TABLE 1.1

WELLCOME CLASSIFICATION OF INFANTILE MALNUTRITION ²

	Percentage of expected weight for age ^*	Oedema
Marasmus	< 60	Absent
Marasmic kwashiorkor	< 60	Present
Kwashiorkor	60–80	Present
Underweight	60–80	Absent

^*Taken as the 50th percentile of the Boston standards.³

McLaren et al.⁴ introduced a simple scoring system for classifying the severe forms only (Table 1.2). This method is precise and provides a means of objectively classifying the type of patients likely to be hospitalized. It does, however, require access to laboratory facilities. Another method, introduced by Kanawati and McLaren⁵, requires only the use of a stiff tape-measure and is based on the ratio of mid-arm circumference to head circumference, which is independent of age at least from 3 months to 48 months and is similar for the two sexes (Table 1.3). This method is, however, rough, unsuitable for use in individual children and is intended for use only in screening large numbers.

TABLE 1.2

SIMPLE SCORING SYSTEM FOR PROTEIN–ENERGY MALNUTRITION⁴

TABLE 1.3

ASSESSMENT OF MARGINAL MALNUTRITION ⁵

^*PEM, protein-energy malnutrition.

It seems desirable that any classification of PEM should take into account deficits in weight and height for age. One such classification is shown in Table 1.4. The diagnosis of the kind of severe PEM with which the child presents, kwashiorkor or marasmus, may change quickly for if oedema is lost a kwashiorkor child becomes a marasmic one.

TABLE 1.4

CLASSIFICATION OF NUTRITIONAL STATUS IN EARLY CHILDHOOD^6†

Classification	Observed weight as percentage of ideal weight/length age
Overweight	> 110
Normal range	90–109
Mild PEM^*	85–89
Moderate PEM	75–84
Severe PEM ^**	< 75

^*PEM, protein-energy malnutrition.

^**Marasmus (no oedema) or kwashiorkor (with oedema).

^†Authors give a nomogram for rapid calculation and classification.

Pathogenesis

Although PEM is a nutritional deficiency disease, it is doubtful if nutrition can ever be separated from the whole variety of social factors that makes up the complex environment in which children grow up. Thus, economic stringencies, overcrowding, poor hygiene, and religious and other taboos all contribute to the development of the condition. The exact form of PEM that develops depends on the age of the child, the duration of breast-feeding and also on weaning practices. Industrialization has influenced the nature of the most prevalent types of PEM in different communities. From an analysis of these factors. in the Lebanon and in Jordan, McLaren⁷ put forward a scheme (Fig. 1.1) to account for the pathogenesis of the extreme forms.

Figure 1.1 Paths leading from early weaning to nutritional marasmus and from protracted breast feeding to kwashiorkor.

Classically it was held that marasmus is caused by a shortage of food, predominantly of energy, and that kwashiorkor is caused by a shortage of protein of the right kind but that the energy supply might be adequate. It has become clear that this simplistic view is a misconception, and that this has had important consequences for it has led to the idea that there is a ‘protein gap’, which has been described, in fact, as a ‘protein fiasco’. In India, children have been described as developing either marasmus or kwas...

Índice

• Cover image
• Title page
• Table of Contents
• Copyright
• CONTRIBUTORS
• Preface
• Acknowledgements
• SECTION 1: GENERAL METABOLIC DISORDERS
• SECTION 2: CLINICAL BIOCHEMISTRY IN THE CARE OF SICK PATIENTS
• SECTION 3: CLINICAL BIOCHEMISTRY OF PREGNANCY AND CHILDHOOD
• SECTION 4: DISORDERS OF THE RENAL TRACT
• SECTION 5: DISORDERS OF THE GASTROINTESTINAL TRACT
• SECTION 6: DISORDERS OF THE BLOOD CONSTITUENTS
• SECTION 7: DISORDERS OF THE NEUROMUSCULAR SYSTEM
• SECTION 8: DISORDERS OF THE CARDIOVASCULAR SYSTEM
• SECTION 9: ENDOCRINE DISORDERS
• SECTION 10: BIOCHEMICAL ASPECTS OF TOXICOLOGY AND PHARMACOLOGY
• Index