A Narrative Review of Natural History of Diseases and Continuity of Care in Family Medicine

Natural history of disease refers to the progression of a disease process in an individual over time. Family medicine has important epidemiological connotations, presenting a unique opportunity to study natural history of a disease. We present an example case of the natural history of the disease: the continued care of a patient with thromboangiitis obliterans for 37 years, who was continuously attended over many years in family medicine level, with the aim of refl ecting and conceptualizing the importance that, for epidemiological knowledge of natural history of diseases have the data provide by family medicine, which can be classifi ed as biopsychosocial typologies of the natural history of diseases, according to their pattern of natural history, and through an epidemiological classifi cation directed by medical intervention. So, there are two complementary perspectives to characterize the natural history of the disease: that of the general practitioner, who through the medical records the entire process of each patient, and can determine both that there is a new health problem and its peculiarities; is an individualized vision. And the epidemiologist, who through the multiple health records he handles, and the support of biostatistics can discover a new disease and its evolution; is a population view. Future epidemiological strategies that use longitudinal study designs or “continuing care”, using homogeneous defi nitions of diseases, could play a pivotal role in better elucidating the controversies in natural history and the pathophysiology of subtypes of many common diseases, leading to improved clinical care. Cohort studies on the natural history of diseases should be enhanced in order to provide a basis for the development of health strategies and prevention and treatment measures. The ordinary general practitioners can make a signifi cant contribution to research on the basis of patients seen in routine practice.


Introduction
Natural history of disease refers to the progression of a disease process in an individual over time, in the absence of treatment. Although at present, the natural history of disease is affected by the medical or surgical treatment, and new drugs are going to change the natural history and epidemiology of many diseases worldwide. However, the global consequences will depend on treatment accessibility, and of medication adherence [1][2][3][4][5]. is an individualized vision. The epidemiologist, who through the multiple health records he handles, and the support of biostatistics can discover a new disease and its evolution; is a population view.
The person is the center of interest for the family doctor; but the importance of epidemiological research at the family physician level is often forgotten. This epidemiological level today is downplayed or underestimated; however, there have been family physician pioneers who studied the epidemiologic problems of their community with scientifi c rigor. Some of them have been recognized for their seminal work in the last 125 years [7][8][9][10][11].
In this context, we present an example-case of the natural history of the disease: the continued care of a patient with thromboangiitis obliterans for 37 years, including selected copathologies. The patient was continuously attended over many years in family medicine level, and it is presented with the aim of refl ecting and conceptualizing the importance that, for epidemiological knowledge of natural history of diseases, have the data provide by family medicine.

Case Example
Thromboangiitis obliterans: a natural history for 37 years 1974: JRM was diagnosed of thromboangiitis obliterans, at 24 years of age, being a smoker of 20 cigarettes / day for 8 years. The onset symptomatology consisted of hypersensitivity to cold, with pain and coldness in both hands and feet. From its diagnosis, the disease followed a progressive course, with ulcerations in the right hand and both feet that forced the amputation of six fi ngers.

1981:
In spite of the indication to suppress the tobacco, the patient did not stop smoking until 7 years after the diagnosis.

1986:
The patient continued medical treatment with antiplatelet agents, peripheral circulation stimulants and calcium antagonists, and a sympathectomy was performed.

1995:
The patient quit smoking.

2011:
The patient presents venous thrombosis in lower right limb. There is sepsis of urinary origin. Pulmonary, bony, thoracic, hepatic, and splenic metastases are found. The patient dies at 60 years of age.

Discussion
The relationship between continuity of care in family medicine and the epidemiological knowledge of the natural history of diseases The continuity of care is considered as a defi ning characteristic of family medicine and primary health care [12][13][14][15][16][17][18], although it can be seen from different perspectives, suggesting a hierarchy of dimensions from less to more complexity (Table 1) [19][20][21][22][23].
In medicine a priority objective of the studies must be the knowledge of the natural history of the disease [24]. Family Table 1: Hierarchy of Continuity Dimensions of Attention.

1) Continuity of information
Is the availability of clinical information to any health care provider who treats the patient 2) Geographical continuity It refers to care provided with continuity, regardless of the location of the patient -consultation, home, hospital, etc.

3) Interdisciplinary or team continuity
It involves the care that allows the prior knowledge of the patient even when it requires a wide range of specialized services

4) Longitudinal or chronological continuity
It refers to the fact that health care is produced in the same place, with the same medical record, and with the same professionals, but does not directly address the nature of the relationship between the patient and the provider  Figure 1) [25][26][27][28]. The simplest and most basic way to achieve effective care is by continuing care [25].

A case example of thromboangiitis obliterans
Although our main interest in this article is not to communicate a clinical case, but to present it as an example of the ideal position of the family physician to observe the natural history of the diseases, thanks to his work of continuous care [25], this clinical observation agrees With other publications where patients were followed for several years, and those who stopped smoking responded better to treatment and evolved more favorably than those who did not [29,30]. Our

The natural history of diseases
The process begins with the appropriate exposure to or accumulation of factors suffi cient for the disease to begin in a susceptible host. For an infectious disease, the exposure is a microorganism. For cancer, the exposure may be a factor that initiates the process, such as asbestos fi bers or components in tobacco smoke (for lung cancer), or one that promotes the process, such as estrogen (for endometrial cancer).
After the disease process has been triggered, pathological changes then occur without the individual being aware of them.
This stage of subclinical disease, extending from the time of exposure to onset of disease symptoms, is usually called the incubation period for infectious diseases, and the latency period for chronic diseases. During this stage, disease is said to be asymptomatic (no symptoms) or unapparent. This period may be as brief as seconds for hypersensitivity and toxic reactions to as long as decades for certain chronic diseases. Even for a single disease, the characteristic incubation period has a range.
For example, the typical incubation period for hepatitis A is as long as 7 weeks. The latency period for leukemia to become evident among survivors of the atomic bomb blast in Hiroshima ranged from 2 to 12 years, peaking at 6-7 years [31].
Although disease is not apparent during the incubation period, some pathologic changes may be detectable with laboratory, radiographic, or other screening methods. Most screening programs attempt to identify the disease process during this phase of its natural history, since intervention at this early stage is likely to be more effective than treatment given after the disease has progressed and become symptomatic.
The onset of symptoms marks the transition from subclinical to clinical disease. Most diagnoses are made during the stage of clinical disease. In some people, however, the disease process may never progress to clinically apparent illness. In others, the disease process may result in illness that ranges from mild to severe or fatal. This range is called the spectrum of disease. Ultimately, the disease process ends either in recovery, disability or death.
Because the spectrum of disease can include asymptomatic and mild cases, the cases of illness diagnosed by clinicians in the community often represent only the tip of the iceberg.
Many additional cases may be too early to diagnose or may never progress to the clinical stage. Unfortunately, persons with unapparent or undiagnosed infections may nonetheless be able to transmit infection to others. The challenge to public health workers is that these carriers, unaware that they are infected and infectious to others, are sometimes more likely to unwittingly spread infection than are people with obvious illness [32].
Man is subject to a great variety of diseases and it has always    "strawberry", growing pains, enuresis, etc. They have high incidence and prevalence during a plateau and a descent to a level of low incidence that is maintained.

2.
Many diseases become more prevalent with age and some become serious. For example: osteoarthritis, coronary heart disease, stroke, peripheral arteriopathy, hypertension, COPD and cancers. There is a plateau of low incidence and prevalence, followed by an increase from the average age of life to a plateau of high prevalence and incidence.
3. Some diseases are "once and always". That is, once they arise they persist all their lives. Example: some congenital diseases such as Down syndrome and cystic fi brosis, and acquired diseases such as diabetes, hypothyroidism, blindness and deafness. They present a constant plateau of prevalence and incidence.
4. Some diseases appear to follow a course and disappear: they tend to appear early in the middle of adulthood.
There is a period of clinical activity, persistent or intermittent, that can last 10-20 years and then the symptoms decrease or disappear. Examples: asthma, migraine, allergic rhinitis, low back pain, duodenal ulcer, anxiety, depression, urinary tract infections in women, and various gynecological problems.

5.
Some diseases with high prevalence and incidence in young and old. They include bronchial hyperreactivity, hydrocele, hernias and constipation.

An epidemiological classifi cation directed by medical intervention
The diseases can be grouped into three blocks, following an epidemiological classifi cation directed by medical intervention [61]: a) Diseases whose etiology is understood suffi ciently for prevention (for example: coronary heart disease, adverse drug reactions, pulmonary tuberculosis, stroke, traffi c accidents).
b) Diseases whose etiology is only partially known but for which there are proposed screening or prevention approaches (for ezample, breast cancer, bladder cancer, prostatic hypertrophy, hypertension and genetic diseases).  The ordinary general practitioners can make a signifi cant contribution to research on the basis of patients seen in routine practice. It does not need the usual obsession for statistics, but an equivalent clinical mentality to that of Alexander Fleming -to realize the patchy shape in Petri disk which turns up in surgery: yeast fl oats through the windows, lands on a plate of germs, and kills them; it is penicillin. The trick is to know what to notice, and what to ignore [72].