SYNCOPE
SYNCOPE: Excerpt from Differential Diagnosis in Primary Care
The differential of syncope or a brief loss of consciousness is best
developed with the use of physiology and, to a lesser extent,
anatomy. Like convulsions , syncope is due to a diminished supply of oxygen and glucose
in the brain cell. Anything that produces hypoglycemia may lead to episodes of syncope,
but the most common cause is overdose of insulin. It is also important to
include insulinomas and overdose of oral hypoglycemic agents (Table
55).
Reduced delivery of oxygen to the brain cell accounts for most cases of
syncope. Oxygen must get into the body through the lungs with adequate
ventilation. It must then be absorbed through the alveolar–capillary
membrane, picked up by an adequate number of red cells, and delivered to the
brain by a good functioning heart and unobstructed carotid and
vertebral–basilar system. Retracing the above physiology and anatomy will
develop the disease entities that must be considered in the differential
diagnosis of syncope.
SYNCOPE
|
| I | C | A | T | E |
|
| Intoxication | Congenital | Autoimmune | Trauma | Endocrine |
|
|
| | Allergic | | |
|
| Tolbutamide Hypoglycemic drugs and insulin |
|
| |
Insulinoma Addison disease
Hypopituitarism |
|
| Pneumoconiosis |
Cystic fibrosis |
Sarcoidosis Anemia |
Pneumothorax |
|
| Drug-induced anemia |
Sickle cell anemia |
Hemolytic anemia Idiopathic thrombocytopenic purpura |
Blood loss |
|
| Cardiac arrhythmias from drugs and alcohol |
|
Rheumatic valvular disease |
|
| Drug-induced postural hypotension |
Anomalous circle of Willis |
|
| | Migraine |
Vasculitis Purpura |
|
Thus, mechanical obstructions of the larynx (foreign body), the bronchi,
bronchioles (asthma and emphysema), or alveolar–capillary membrane
(pulmonary fibrosis, sarcoidosis, or pulmonary embolism) may cause anoxia
and syncope. Severe anemia prevents the adequate transport of oxygen. Oxygen
transport from the heart to the brain may be obstructed mechanically or
functionally. It is functionally obstructed by CHF of Stokes–Adams syndrome
(heart block) and other arrhythmias, particularly ventricular tachycardia
and sick sinus syndrome. Functional obstruction may result from a drop in
blood pressure from carotid sinus syncope, postural hypotension , and vasovagal syncope. True
vertigo may lead to
syncope by way of the latter mechanism.
Mechanical obstruction may occur at the aortic valve (aortic stenosis or
insufficiency), at the carotid arteries (thrombi or plaques), or focally in
the smaller arteries from ischemia due to arterial thrombi or emboli. Less
commonly, mechanical obstruction may occur from ball–valve thrombi in the
mitral or tricuspid valve, large pulmonary emboli, or cough syncope in which
poor venous return to the heart is the cause.
Approach to the Diagnosis
Clinical differentiation of the various forms of syncope is made by
combinations of symptoms. Thus, syncope with marked sweating and tachycardia
is more likely due to hypoglycemia. Syncope with sweating and bradycardia is
more likely due to vasovagal syncope. Focal neurologic signs during the attack suggest
transient ischemia attack (TIA) and prompt
a search for sources of emboli or thrombosis (sickle cell disease,
polycythemia, or macroglobulinemia). Transesophageal echocardiography is the
procedure of choice to find a cardiac source. A family history of syncope
suggests migraine, epilepsy, or vasovagal attacks. Epilepsy is a strong
possibility in the young, whereas heart block is more likely in the aged.
Consequently, an EEG and Holter monitoring are useful in the workup.
Other Useful Tests
-
CBC (anemia)
- Chemistry panel (hypoglycemia, hypocalcemia)
- Serum and urine osmolality (dehydration)
- Upright-tilt table test (postural hypotension)
- ECG (cardiac arrhythmia)
- Carotid sinus massage (carotid sinus syndrome)
- ECG (CHF, valvular heart disease)
- Carotid scans (TIA)
- Four-vessel cerebral angiogram (TIA)
- Exercise tolerance test (coronary insufficiency)
- Signal-averaging ECG (ventricular arrhythmia)
- 72-hour fast with glucose monitoring (insulinoma)
- Drug screen (drug abuse)
- 24-hour ambulatory blood pressure monitoring (postural
hypotension)
- Neurology consult
- Continuous-loop ECG recording (cardiac arrhythmia)
- Psychiatric consult
- Electrophysiologic study (cardiac arrhythmia)
