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Background
reading for 3rd year medical students at the Faculty of Medicine
King Fahad Medical City by Professor Omar Hasan Kasule MB ChB(MUK), MPH
(Harvard), DrPH (Harvard) on September 9, 2013
1.0 DIAGNOSIS
1.1 Definition
The term diagnosis
is derived from the Greek word ‘gnosis’ which means knowledge. It basically
refers to determining if a disease or disorder exists and to define its nature.
It involves analysis of data on symptoms, signs, and specific investigations.
Background knowledge of disease epidemiology and disease risk factors in an
area at a given point in time helps in arriving at a correct diagnosis.
1.2 Probability in diagnosis
It may not be
possible to reach conclusion about one diagnosis and one may have to identify
several diagnoses and arrange them in order of likelihood. Therapeutic
interventions are undertaken on the basis of a leading diagnosis and alternate
diagnoses. The legal basis for intervention in such cases is ghalabat al dhann or predominant
conjecture. Further manifestations of the disease process or response to
therapy may finally allow definitive determination of the diagnosis. There are
situations in which the final diagnosis cannot be determined until after death
when post-mortem examination reveals the true cause of death.
1.3 Basis of diagnosis
Historically
diagnosis relied more on symptoms. With development of systematic methods of
clinical examination more reliance was placed on signs. However major breakthroughs
in diagnosis were achieved when medical technology provided a wide array of
accurate and reliable laboratory and radiological investigations. Instruments
were also developed to be able to make more accurate observation of signs both
inside and outside the body. Further refinements in diagnosis are going to be
based on technological developments but will never supplant the role of careful
history taking for symptoms and clinical examination for signs.
1.4 Use of computers
Computers are being
used increasingly in the diagnostic process to process and summarize massive
volume of quantitative data and compute probabilities of various diagnostic
possibilities. The human mind is still needed to make the final diagnosis
because the computer in the end is a machine and does not fully encompass all
the creative and innovative thinking skills found in a human physician.
Physicians acquire diagnostic competence through long periods of practical
clinical training because in the end medicine is an art. Computers and other
machines cannot have this clinical competence.
1.5 Hypotheses
Making a diagnosis
requires summarizing and analyzing information collected from history, physical
examination, and various investigations. The clinician initially develops a series
of possible alternative diagnoses called the differential diagnosis. With use
of further information from investigations or sometimes response to therapy,
the diagnostic possibilities are narrowed down even further. Sometimes a
diagnosis is arrived at by elimination. Computers using algorithms developed by
experienced clinicians can be used to aid the diagnostic process.
2.0 CLINICAL HISTORY
2.1 Consent
and confidentiality
Patients have to consent before their medical history
can be taken otherwise the physician will be trespassing on privacy and may be
accused of spying, tajassus. The permission to take history is needed
even if a proxy such as a spouse or a parent volunteers the history. The same
applies to information collected from previous records. Any information
obtained from or about a patient is confidential and its unauthorized
disclosure is a breach of confidentiality.
2.2 Nasiihat and Da’awat
The purpose of
history taking is to discover the social or personal antecedents of disease as
well as the natural history of the disease. This involves considerable probing
into personal life and privacy. It provides a golden opportunity for both
physician and patient to face diseases of the heart, amraadh al qalb, that affect physical health. The diseases of the
heart may be transgression, dhulm;
neglect, ghaflat; loss of
self-control and following passions (sex, drug, and alcohol-addiction). There
is an opportunity for the physician to exercise the function of da’wah and for
the patient to make repentance, taubat.
2.3 Legal issues
History taking is
also an opportunity for discovery of legal complications such as foster
relations that prohibit marriage, defective marriages concluded during ‘iddat. In complicated medical
conditions, history taking may be an opportunity for discussing costs of
medical care with the patient. The physician taking history may face a major
ethical dilemma when in the course of taking history, the patient volunteers
information about a criminal action that should be prosecuted. If the physician
keeps the information to himself, he is not fulfilling the duty required of him
as a citizen to report crime to the authorities.
2.4 Communication skills
Successful history
taking requires good communication skills and careful observation of non-verbal
clues. Accurate history depends on the honesty and memory of the patient.
Patients may not want to reveal some information that they consider
embarrassing or that they mistakenly consider irrelevant to the presenting
disease condition. Patients may forget some information or confuse it. The
interviewer must be tactful and sensitive in probing for relevant information
and may have to adopt various strategies to help the patient’s memory.
Questions may be open-ended or closed. Sometimes the interviewer may just have
to keep quiet and listen actively as the patient talks to be able to pick up
useful clues. Interrupting patients is a frequent problem of interviewers who
pressed for time would like to keep the interview as short as possible. Patients
with underlying emotional problems may only verbalize physical symptoms and it
requires tact and establishment of rapport to get them to talk about their
inner worries and feelings.
2.5 Elements of a medical history
A complete medical
history consists of an account of the present illness and its evolution since
first noticed, relevant past medical history, family history, social history,
psychological history, and history of occupational and environmental exposures.
Account of the
presenting illness covers recent changes in health status, associated
triggering factors, and all changes that have occurred from the start until
presentation to the physician. The account is not completed on the first
interview. In the course of clinical examination or treatment signs may be
identified that suggest eliciting more information about the causes and course
of the presenting illness.
Past medical
history covers health status and disease experiences as back as can be
remembered. It includes medical, surgical, and psychiatric conditions. Both
severe illnesses requiring hospitalization and less severe ones treated
symptomatically or not treated at all need to be recorded if they have
relevance to the presenting illness. The interviewer must have an extensive knowledge
of disease epidemiology and disease pathophysiology to known what relevant
questions to ask.
Family history
elicits information about diseases in immediate family members because the
presenting illness may have a familial hereditary basis or an environmental
basis in the domicile of the patient.
Social history
elicits information about social factors that are relevant to disease such as
marital status, education, lifestyle (eg alcohol, drugs, smoking), and beliefs.
Occupational and
environmental exposures should be documented for a long time before the
presenting illness because for chronic diseases the causative agent may act
years before the presenting illness.
History taking is
completed by a thorough review of the organ systems. The patient is asked
specific questions about symptoms in each system that may have relevance to the
presenting complaint.
3.0 CLINICAL STATE EXAMINATION
3.1 Consent
and confidentiality
The issues of consent and confidentiality discussed
above for history taking are also relevant to clinical or mental examinations.
A patient can only be examined against his or her consent only if there is a
necessity, dharuurat. The necessity may relate to the life of the
patient or may be in public interest such as examining a suspected criminal for
evidence about the crime. Mental patients can are not legally competent to give
consent; the necessary consent could be obtained from a guardian, wali.
Examination by a caregiver of the opposite gender requires special
consideration. It is always preferable that physicians of the same gender carry
out the examination. A physician of the opposite gender can be used only if a
situation of necessity arises. A chaperone must be present. Examination limited
to what is necessary. Al nadhar ila al
awrat bi qadar al dharuurat.
The physician should allay the anxiety of patients
being examined.
3.2 Contents
of physical examination
Clinical examination traditionally consisted of
inspection, palpation, percussion, and auscultation. These processes have now
become more sophisticated because of availability of various diagnostic
instruments developed by modern medical technology.
Inspection is
visual observation before touching a patient. The following are the main points
of observation: general appearance, nutritional status, symmetry, posture,
wounds and signs of external injury, mood and behavior. Many useful clues can
be obtained from looking at various parts of the body. Hair loss may indicate
infection, hormonal disturbances, or anti-cancer chemotherapy. Clubbed nails
indicate chronic cardiovascular or respiratory disease. Pitted nails indicate
psoriasis. The skin may have benign moles or malignant cancers.
Palpation is using the physician’s hand and sense of
touch to elicit signs from structures on the surface of the body or organs
inside the body. Light palpation can detect tenderness, muscle spasm, rigidity
and hardness. Deep palpation can define the size, shape, and consistency of
internal structures. Vibratory sensations can also be detected on palpation.
Percussion involves tapping on the surface and
listening to the sound produced. Internal structures filled with air, water, or
solidified tissue have different resonances that a trained examiner can
identify and characterize.
Auscultation is listening to sounds from the heart,
blood vessels, lungs, and intestines. Normal sounds made by closure of the
various heart valves can be heard and can be distinguished. Murmurs indicate
abnormal blood flow in the heart. Bruits are produced when blood flows through
an occluded blood vessel. In a healthy lung air flows smoothly producing normal
breath sounds. Wheezes are produced in cases of obstruction. Crackles (also
called rales) are produced when there is excessive fluid in the lungs.
Inflammation of the pleura produces creaking sounds. No sounds are heard when
the bowel is paralyzed and there are no bowel movements. In intestinal
obstruction high pitch sounds are heard. In intestinal hyperactivity the sounds
are greatly enhanced.
In an emergency, the sequence of history-taking and
physical examination described above cannot be followed. Priority is given to
examining the respiratory, circulatory, and nervous systems because they are
essential for life. The respiratory system is examined to assure that there is
adequate oxygenation. The circulatory system is examined to ensure that there
is an adequate cardiac output. The nervous system is examined by observing
response to external stimulation. The size and reaction of pupils to light
indicate the state of consciousness.
3.3
Pediatric examinations
Pediatric examinations involve additional
observations. The Agar score is assessed at birth and indicates overall
prognosis. Growth is assessed as height and weight being compared to standard
charts. At birth the average length is 50 cm. It increases by 50% at 12 months
and doubles at 4 years. From year 2 until the adolescent growth spurt height
increases by 5 cm every year. Birthweight doubles at 4-5 months and triples at
12 months. It increases by 2.3 kg every year from year 2 to the adolescent
growth spurt. The Denver Developmental Screening Test assesses psycho-social
development that includes language and social skills. Children are also
examined for vision, hearing, and dental development.
3.4 Geriatric
examination
Geriatric examinations call for special skills. With
age there are changes in body structure and function. Cardiac changes include
reduced cardiac output and decreased blood flow to the organs. Respiratory
changes are decrease of alveoli and weakening of respiratory muscles.
Gastro-intestinal changes include: decreased gastric acid secretion, decreased
intestinal motility with frequent complaints of constipation, slower drug
metabolism, and loss of teeth resulting in impaired mastication and chewing of
food. Excretion is decreased with lower urinary output associated with a
decreased number of nephrons. Musculoskeletal changes are decreases muscle
mass, and osteoporosis. Endocrine changes are decreased thyroid and adrenal
function, decrease insulin production, and increased insulin resistance.
Neurological changes are slower nerve conduction, loss of brain mass, decrease
cerebral blood flow, depression, decreased sleep, and dementia. Sensory changes
are: decreased visual acuity, decreased smell and taste sensation. The elderly
become shorter because of narrowing of intervertebral discs.
3.5 Mental state examination
Psychiatric examination assesses stress, anxiety
disorders, mood disorders, and psychotic disorders. Anxiety disorders include
panic disorder, generalized disorder, post-traumatic stress disorder, phobic
disorder, and obsessive-compulsive disorder. Mood disorders are major
depression, dysthymia (minor depression), bipolar disorder, and cyclothymia
(chronic minor form of the bipolar disorder).
Psychological tests are used in psychiatric diagnosis.
The Minnesota Multiphasic Personality Inventory (MMPI) is a questionnaire used
to assess personality characteristics. The Mini-Mental State Examination
assesses cognitive function. The Rorschach test assesses personality
functioning and emotional aberrations.
The Thematic Appreciation Test (TAT) assesses anxiety, personal
conflict, and interpersonal relations. Depression is assessed using the Beck
Depression Inventory and the Zung Self-Rating Depression Scale.
4.0 LABORATORY INVESTIGATIONS
4.1 Purpose
The purposes of laboratory investigation are
to provide base-line information, establish a diagnosis, exclude alternative
diagnoses, evaluate severity, plan treatment, and predict prognosis. Results of
laboratory tests are used in the process of decision making at all stages of
clinical management. Usually treatment is based a provisional diagnosis. The
final or discharge diagnosis is confirmed towards the end of the disease
episode. The test must be sensitive and specific. Due to availability of
automatic processing of biological samples physicians no longer ask for
specific tests but ask for a battery of tests. This risks producing false
positive results on the basis of chance alone. The range of normal results
varies with the test technique and with age or race. The results of
laboratory investigations have the same requirements for confidentiality as
history and clinical examination.
4.2 Types of
investigations
Hematological
investigations are carried out for anemia, hemoglobinopathies, bleeding
disorders, blood grouping, and blood compatibility. A complete blood count
(CBC) consists of number of red blood cells, number of white blood cells with a
differential count, hemoglobin concentration, hematocrit, red cell volume
(MCV), and platelet count. Coagulability is assessed by the prothrombin test,
the partial thromboplastin time, plasma fibrinogen, and blood clotting factors.
The erythrocyte sedimentation rate (ESR) is a non-specific indicator of
inflammation. The Coombs or antiglobulin test (AGT) tests red blood cell
compatibility for purposes of transfusion.
Histopathological
diagnosis describes the pathological process and indications of possible
initial insults.
Microbiological
investigations are bacteriological, virological, and parasitological.
Biochemical
investigations include renal function tests, liver function tests, fluids,
electrolytes, and acid-base balance. Fasting blood glucose level and the
glucose tolerance test are used to diagnose diabetes mellitus. Gastrointestinal
absorption is assessed by measuring urinary excretion of ingested radioactive
substances or urinary excretion of D-xylose, a substance that is not
metabolized by the body. Intestinal absorption can also be assessed by the
amount of fat in stool collected over 3 days following a fat-rich diet. Levels
of various toxins are measured in serum or other body fluids using specialized
biochemical tests.
Immunological
tests assess presence and concentration of antibodies.
Genetic/chromosomal
analysis is used increasingly in disease diagnosis. Careful family history
taking and physical examination are used to construct a family pedigree for a
specific disease. Among specific genetically-related tests are: chromosome karyotyping,
enzyme assays, hormonal assays, aminoacid assays, blood grouping and typing,
immunoglobulin assays, and hemoglobin electrophoresis. Prenatal tests for
congenital genetic disease is controversial because it encourages abortion.
Genetic tests pose a special problem because genetic findings in a patient give
information about genetic make-ups of parents and siblings. Thus disclosure of
the patient’s genetic findings may require in addition the consent of the
relatives concerned.
Biological
markers are used in diagnosis and follow up of disease treatment the
commonest being: HCG for trophoblastic tumors & hepatocellular carcinoma;
AFP, HCG, HBD, PLAP for germ cell tumors; CEA for GIT tumors, CA125 for ovarian
cancer; PSA for prostate cancer; CA and S-3 for breast cancer; and SCC for skin
cancer. analysis is used increasingly in
disease diagnosis.
Urine
examination includes assessment for color, turbidity, cells, urinary casts,
specific gravity, bilirubin, urobilinogen, hemoglobin, glucose, ketone bodies,
pH, protein, and bacteria.
Fecal
examination consists of fecal occult blood testing (FOBT), culture for
microorganisms, and examination for parasites.
Cerebrospinal
fluid is examined for white blood cells, culture for microorganisms,
glucose, protein, and fluid pressure. Gastric juice is examined for blood and
is cultured for microorganisms.
Semen is
examined for number, motility, and normality.
5.0 RADIOLOGICAL/IMAGING INVESTIGATIONS
5.1 Non-invasive investigations
Radiological
investigations reveal a lot of information with minimal invasion. The commonest
radiological examination is the plain X-ray film. It may be enhanced by used of
barium or air to show inside structures better. Computed tomography (CT scan)
produces a cross-section of the body at various levels. Ultrasonography uses sound waves to define
internal structures. It is quick and cheap but is not as accurate as CT scan or
MRI. Magnetic resonance imaging (MRI) uses magnetic fields and radiowaves to
produce images of internal structures. It is more accurate than CT scan but is
more expensive and more cumbersome to use. CT can and MRI produce 2-dimensional
images but newer techniques are able to produce 3-dimensional images.
Mammography is used to screen for breast cancer. The results of radiological
investigations are confidential. Images that show the shape of the body parts
can be considered showing awrat and should not be seen except by authorized
people only and for specific purposes. Digital subtraction angiography and positron
emission tomography are also used.
5.2 Invasive investigations
Invasive investigations carry a higher risk to the
patient; their benefits should be carefully weighed against the benefits. The
commonest investigations are: endoscopy (nasophayngolaryngoscopy, colonoscopy,
sigmoidoscopy, esophagogastroduodenoscopy, cholangiopancreatoscopy, colposcopy,
and peritoneal laparascopy), cardiac catheterization and angiography, biopsy
(incision, excision, needle, aspiration, and abrasion as in the Pap smear test),
autopsy, and diagnostic / exploratory laparatomy. These investigations should
be carried out only if there is a clear necessity, dharuurat.
6.0 INSTRUMENTAL
INVESTIGATIONS
The
electrocardiogram (ECG) assesses cardiac electrical conduction. The electroencephalogram
(EEG) measures electrical activity in the brain. The echocardiogram uses sound
waves to assess structure and movement of the heart and is more useful in
children. Myocardial perfusion imaging uses radioactive thallium injected
intravenously to study heart pathology detected by disturbance in radioactive
uptake. Electromyography assesses electrical conductivity in muscles.