by Julio Libman and Jesús Ramón Giraudo

Body weight loss is a clinical manifestation of numerous pathological processes that can lead to a decrease in weight mass through various mechanisms. Weight loss of more than 10 kilograms is generally associated with marked changes in physical appearance and can lead to manifestations of malnutrition. Cachexia is defined as a weight decrease greater than 40% below normal in relation to sex, age and height. Secondary weight loss, unlike constitutional thinness, can be accompanied by asthenia and fatigability, low blood pressure, insomnia or drowsiness, depression, menstrual disturbances, reduction of subcutaneous cell tissue and muscular atrophy. In cachexia these manifestations acquire greater magnitude,

Physiology and pathophysiology

In normal people, weight stability is maintained because intake is balanced with caloric expenditure by the coordinated action of feeding centers and satiety, located in the central nervous system. Energy expenditure is divided into three categories: 1) calories necessary to maintain basal metabolism, defining as such the total caloric requirement with the body in a supine and immobile position. In other words, it is the energy required to maintain the functional and structural integrity of the organism in the absence of physical activity. Approximately 50% of daily calories are consumed in this process; 2) calories necessary for the absorption of food, the so-called specific dynamic action, which involves 10% of the total intake in non-obese and active individuals,

The organism is made up of four main compartments: the protoplasm, which represents from 30 to 35 kg, the extracellular fluid with 15 to 16 kg, the bone tissue with 4 to 5 kg, and the adipose tissue, which comprises from 14 to 18 kg . The first three compartments represent lean mass, which constitutes 75 to 80% of body weight. The rest corresponds to fatty tissue, which performs important energetic, endocrine, metabolic and thermal functions.

Weight loss is determined by a negative balance between intake and caloric expenditure. Weight loss may reflect a decrease in tissue mass or in the body's liquid content. A rapid decline more likely indicates the latter. In this sense, three circumstances can be distinguished: 1) decrease in food and liquid intake; 2) increased caloric expenditure, and 3) excess loss of nutrients and liquids.

Weight loss can be, in multiple circumstances, the result of the combination of two or more of these mechanisms. Sometimes weight loss due to decreased tissue mass is disguised by simultaneous fluid retention, as occurs in the patient with cirrhosis who develops ascites or in anorexia nervosa due to concomitant edema.

Causes of weight loss

Weight loss, in addition to voluntarily decreasing intake and / or increasing physical activity, can be due to a number of causes, including:

1. Endocrine diseases. They include Addison's disease and eventually panhypopituitarism, attributable in these circumstances to anorexia caused by cortisol deficiency. The most frequent and characteristic example is given by hyperthyroidism. In this case, there is a concomitant increase in caloric intake, which can sometimes lead to weight gain, however, the large increase in caloric expenditure due to increased metabolic rate and motor activity. The thyroid hormone would produce an increase in the activity of sodium and potassium ATPase in different tissues, which suggests that the decreased efficiency of the calories ingested would be due to futile cycles of synthesis and degradation of ATP with loss of energy in the form of heat. . Severe hypercalcemia, through anorexia, nausea,

2. Diabetes mellitus . Weight loss may be due in part to glucosuria-induced osmotic diuresis. It can also occur mainly in insulin-dependent diabetes, due to caloric loss through glucosuria and insulin deficiency that results in less synthesis and greater catabolism of fats and proteins. Except in ketoacidosis states, weight loss is frequently associated with polyphagia. The decrease in the use of carbohydrates causes a state of hydrocarbon starvation and, by a not completely clarified mechanism, the hypothalamic centers are affected, which induces an increase in the desire to eat.

3. Tumors. Weight loss, sometimes without concomitant symptoms and without apparent cause, is one of the classic manifestations of the existence of a neoplasm. The digestive system is the most common site of hidden cancer development. Other patients with malignant tumors present weight loss associated with other signs and symptoms that report serious pathology. Multiple reasons can determine the weight loss in advanced cancer, such as anorexia (linked, among other factors, to acidosis, pain from chronic depression), nausea, vomiting, and hypermetabolism. In some malignancies, especially lymphomas, there is decreased intestinal absorption. When bleeding occurs, iron, electrolyte, and protein depletion occurs. Ulcerations and infections aggravate the picture,

4. Diseases of the mouth and pharynx . These include painful lesions of the mouth such as those caused by vitamin deficiencies, connective tissue diseases, candidiasis, diphenylhydantoin gingivitis, and heavy metal poisoning. Neurological diseases that alter the ability to chew and swallow, such as strokes, muscular dystrophies, and amyotrophic lateral sclerosis also cause weight loss. So do the lack of teeth and mobile dental prostheses, which alter the intake of nutrients.

5. Gastrointestinal diseases . Among the pathologies that cause weight loss are: a) steatorrhea due to sprue, chronic pancreatitis or cystic fibrosis, however, the increase in intake that can be observed; b) chronic diarrhea due to parasites or inflammatory bowel diseases; c) esophageal diseases with obstruction, dysphagia and reflux, d) acute and chronic hepatitis, cirrhosis.

6. Infections . They include tuberculosis, mycoses, bacterial endocarditis, and amoebic abscesses. The mechanisms would be anorexia and the increased metabolic demands induced by the infection.

7. Psychiatric illnesses . Weight loss can occur in depressive states and in schizophrenia; the most characteristic example is anorexia nervosa, which generally occurs in adolescents and young women.

8. Kidney diseases with uremia . Anorexia is one of the first manifestations of kidney failure, which can contribute to weight loss.

9. Cardiac cachexia . In severe heart failure, there may be weight loss and cachexia attributable to several factors: a) increased metabolism, due to the increased work of the respiratory muscles and the increased demand for 02 by the hypertrophied heart; b) anorexia, nausea and vomiting due to central causes or due to liver congestion and a feeling of fullness in the abdomen, and c) alteration of intestinal absorption due to venous stasis.

10. Socioeconomic factors . Malnutrition is frequent in Latin American countries and, in turn, in elderly people who live alone and in patients who follow incomplete diets prescribed by doctors or imposed by fashion. Weight loss induced by the ingestion of alcohol and drugs that are not accompanied by an adequate intake of nutrients.

11. Medications . Digitalis and amphetamines, among others, induce ñanorexia.

Interrogation and diagnostic methodology

In the course of the interrogation, data will be collected on the maximum weight corresponding to adulthood, the previous weight of the disease, the current weight and the period elapsed since the decrease in weight mass was noted. The existence of polyphagia or anorexia, vomiting, diarrhea or changes in bowel movements, polyuria, cough, dyspnea, expectoration, hemoptysis, chest or abdominal pain, food oddities, anxiety or depression, use of medications and presence of symptoms of hypermetabolism, such as fever, perspiration, palpitations, tremors, etc. Since weight loss is a non-specific manifestation and common to a large number of diseases, the questioning must be complete and systematized. The diagnosis methodology, for these same reasons, will be guided according to the diagnostic impression arising from the interrogation and the physical examination. Thus, for example, the existence of weight loss with fever, chest pain, hemoptoic expectoration and profuse perspiration guides research towards pulmonary tuberculosis (radiology, sputum examination). The presence of abdominal discomfort and changes in the intestinal habit forces the search for a digestive neoplasm (laboratory, radiology, ultrasound, endoscopic examinations). Symptoms of hypermetabolism such as tachycardia, tremor, nervousness and the presence of a goiter lead to hyperthyroidism (131I uptake, thyroxine and triiodothyronine dosing). The association of weight loss with polyuria and polydipsia forces to rule out diabetes mellitus (glycemia, glycosuria). 4 If not found, through questioning and physical examination, a cause that explains the weight loss, the study to be carried out should include: complete blood count, erythrocyte sedimentation. uremia, ionogram, urinalysis, thyroxine and triiodothyronine dosing, glucid tolerance curve, parasitological and occult blood examination in fecal matter, and a radiological pair of the chest (forehead and profile). If the symptom remains without a logical explanation, the following studies should be considered: PPD, serological examinations (latex reaction, VDRL, LE cells, antinucleus factor), proteinogram by electroephoresis and immunoelectrophoresis, hormonal studies to rule out Addison's disease, hypopituitarism, pheochromocytoma and hyperparathyroidism, radiological gastrointestinal, urinary tract, and bone examinations, radioisotope studies,

Fundamentally, the patient's evolution should be closely followed, keeping an eye out for any signs or symptoms that may be added to the clinical picture. In this sense, it is important to have the collaboration of the patient, who must be informed of the reasons for the studies requested.