Differentials
Common
Myocardial infarction
History
central chest pain, radiation to left arm, history of exertional chest pain; smoking, hypercholesterolemia; family history; diabetes mellitus; high BP
Exam
signs of heart failure; jugular venous distention, basal crackles on lung auscultation; heart murmur
1st investigation
Other investigations
- echocardiography:
regional wall abnormalities and valvular abnormalities
Heart failure
History
shortness of breath, ankle swelling, orthopnea, paroxysmal nocturnal dyspnea, history of cardiac risk factors, previous myocardial infarction, valvular heart disease
Exam
jugular venous distension, orthopnea, lower extremity swelling, crackles in the chest on auscultation, increased respiratory rate, S3 gallop rhythm on cardiac auscultation
1st investigation
- echocardiography:
depressed ejection fraction, decreased systolic left ventricular function
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Beta-blocker and other drug-related toxicity
History
prior hypertension or heart disease being medically treated with a beta-blocker, a calcium-channel blocker, or a class 1c antiarrhythmic such as flecainide; syncope and lightheadedness; weakness; loss of appetite
Exam
weak pulse, pulmonary rales, slow heart rate (beta-blockers), peripheral edema, signs of poor skin perfusion
1st investigation
- ECG:
bradycardia, increased PR interval
- urine drug screen:
presence of drug in urine
Other investigations
- serum levels for suspected drugs:
drug level
Hemorrhage, external or internal from any site
History
external injury such as laceration; vomiting blood or bloody stools; melena; vaginal blood loss; or pelvic pain in a woman of childbearing age
Exam
tachycardia; lightheadedness; pale fingernail beds and signs of poor skin perfusion; weak pulse; decreased urine output
1st investigation
- hemoglobin/hematocrit:
low blood count
- stool guaiac test for blood:
presence of blood in stool
- examination of vomitus for blood:
presence of blood in vomit
Other investigations
- serum lactate:
>18 mg/dL (>2 mmol/L) abnormal; >36 mg/dL (>4 mmol/L) associated with higher mortality
- base deficit:
<-2
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Trauma with external or internal hemorrhage
History
injury either blunt or penetrating; fall or crush injury
Exam
tachycardia; lightheadedness; pale fingernail beds and signs of poor skin perfusion; weak pulse; decreased urine output
1st investigation
- FAST (focused assessment with sonography for trauma):
may reveal free fluid in abdominal cavity, or pneumothorax
- chest x-ray:
hemothorax
- hemoglobin/hematocrit:
low blood count
- CT scan thorax:
evidence of hemorrhage
Other investigations
- serum lactate:
>18 mg/dL (>2 mmol/L) abnormal; >36 mg/dL (>4 mmol/L) associated with higher mortality
- base deficit:
<-2
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Gastrointestinal fluid losses
History
vomiting, diarrhea, prolonged symptoms, more common in children
Exam
dry skin and mucosa, loss of skin turgor, decreased urine output
1st investigation
- CBC:
elevated WBC count if infectious cause of diarrhea and vomiting
- serum chemistries:
increased BUN/creatinine
- trial of fluids (oral or intravenous):
clinical improvement with fluid resuscitation
Other investigations
- stool evaluation for culture, organisms, or antibodies:
positive if infectious cause
Intestinal obstruction with fluid third spacing
History
abdominal pain and distention, nausea, vomiting, absolute constipation, previous history of abdominal surgery, lack of passing flatus
Exam
hyperdynamic or absent bowel sounds, hernia, distended tympanic abdomen
1st investigation
- abdominal x-ray:
dilated loops of bowel with multiple fluid levels
Other investigations
- CT abdomen:
dilated loops of bowel, transition point at level of obstruction from collapsed to dilated bowel, cause for obstruction, such as mass, may be evident
Pancreatitis with fluid third spacing or hemorrhage
History
epigastric abdominal pain; radiation to the back; history of gallstones, alcohol abuse, use of steroids; hyperlipidemia; previous episodes
Exam
epigastric tenderness with guarding and rebound; ecchymosis around umbilicus (Cullen sign), ecchymosis in flanks (Grey-Turner sign)
1st investigation
- serum lipase or amylase:
>3 times the upper limit of the normal range
More - LFTs:
usually elevated if gallstones are the cause
Burns
History
children and older people are at risk
Exam
erythema, cellulitis, clouded cornea; burns: dry and painful (first degree), wet and painful (second degree), dry and insensitive (third degree), affecting subcutaneous tissue, tendon, or bone (fourth degree)
1st investigation
- CBC:
low hematocrit, hypovolemia, neutropenia, thrombocytopenia
More - metabolic panel:
high levels of BUN, creatinine, glucose; hyponatremia, hypokalemia
More - carboxyhemoglobin:
high levels
More - arterial blood gas:
may show hypoxia
More - fluorescein staining:
damaged corneal epithelial cells
- CT scan of head and spine:
brain injury, fracture
More - wound histology and biopsy culture:
infection
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Other investigations
Excessive renal loss
History
use of diuretic medications; poorly controlled diabetes mellitus with polyuria
Exam
weakness, lightheadedness, tachycardia, dry mucous membranes, signs of poor skin perfusion
1st investigation
- urine osmolality:
unconcentrated
- urine electrolytes:
sodium loss
Other investigations
Pulmonary embolism
History
chest pain; shortness of breath; recent surgery or immobilization; active malignancy; recent long flight; known deep vein thrombosis; known prothrombotic tendency; use of oral birth control pill
Exam
possible cyanosis, respiratory distress with use of accessory muscles, lung auscultation normal; jugular venous distention if large embolism; calf tenderness, tachycardia, low oxygen saturations
1st investigation
- CT pulmonary angiogram (CTPA) or multidetector CT scan:
clots in the pulmonary arteries
More - ventilation/perfusion lung scan:
may show an area of ventilated lung that is not being perfused
Other investigations
- D-dimer:
elevated
- duplex of leg veins:
positive for deep vein thrombosis
Septic shock
History
symptoms of localized infection, nonspecific symptoms include fever or shivering, dizziness, nausea and vomiting, muscle pain, feeling confused or disoriented; may be history of risk factors include, for example, recent surgery or invasive procedures, immunosuppression, pregnancy or postpartum period, frailty, intravenous drug use, or breach of skin integrity
Exam
tachycardia, tachypnoea, hypotension, fever >100.4˚F (38˚C) or hypothermia <96.8˚F (36˚C), prolonged capillary refill, mottled or ashen skin, cyanosis, low oxygen saturation, newly altered mental state, reduced urine output
1st investigation
- blood culture:
may be positive for organism
More - serum lactate:
may be elevated; levels >18 mg/dL (>2 mmol/L) associated with adverse prognosis; even worse prognosis with levels >36 mg/dL (>4 mmol/L)
More - CBC with differential:
WBC count >12 × 10⁹/L (12,000/microlitre) (leukocytosis); WBC count <4 × 10⁹/L (4000/microlitre) (leukopenia); or a normal WBC count with >10% immature forms; low platelets
More - CRP:
elevated
- blood urea and serum electrolytes:
serum electrolytes may be deranged; blood urea may be elevated
- serum creatinine:
may be elevated
More - liver function tests:
may show elevated bilirubin, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and gamma glutamyl transpeptidase
More - coagulation studies:
may be abnormal
- ABG:
may be hypoxia, hypercapnia, elevated anion gap, metabolic acidosis
Other investigations
- ECG:
may show evidence of ischemia, atrial fibrillation, or other arrhythmia; may be normal
More - CXR:
may show consolidation; demonstrates position of central venous catheter and tracheal tube
- urine microscopy and culture:
may be positive for nitrites, protein or blood; elevated leukocyte count; positive culture for organism
- sputum culture:
may be positive for organism
- lumbar puncture:
may be elevated WBC count, presence of organism on microscopy and positive culture
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Anaphylaxis
History
known allergy; new drug or food ingestion; immunization; recalls bite or sting; rapid development of symptoms; shortness of breath; facial swelling; hypotension, tachycardia, and agitation
Exam
facial edema, tongue swelling, respiratory distress, wheezing , rash, weals, erythema
1st investigation
- trial of intramuscular epinephrine:
Improvement in symptoms
Other investigations
- serum tryptase level:
may be elevated
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Poisoning and adverse drug reaction
History
ingestion of potential poison often with vomiting or diarrhea; medication that is associated with shock as a potential adverse reaction; potential drug interactions (such as nitrates for cardiac disease and drugs used for erectile dysfunction)
Exam
tachycardia; lightheadedness; pale fingernail beds and signs of poor skin perfusion; weak pulse; decreased urine output
1st investigation
- urine and serum drug screen:
drug in urine and serum
- acetaminophen serum levels:
acetaminophen in serum
- salicylate serum levels:
salicylate in serum
Other investigations
- x-ray abdomen:
pills visualized
- serum osmolar gap:
evidence of alcohols
Uncommon
Cardiomyopathy
History
shortness of breath on exertion; history of heart failure; viral infections; alcohol abuse; family history
Exam
evidence of heart failure; jugular venous distention, hepatomegaly, pedal edema, rales in lung bases; accessory muscle use; diminished peripheral pulses
1st investigation
- echocardiography:
reduced ejection fraction, increased left ventricular muscle mass
Other investigations
- B-type natriuretic peptide:
>100 nanograms/L may indicate heart failure
Cardiac valve disease
History
rheumatic fever, spiking fevers, or new murmur suggestive of endocarditis, recent myocardial infarction, bicuspid aortic valve, shortness of breath on exertion, syncope
Exam
mitral facies, heart murmur on auscultation, rales at lung bases, spiking temperatures if endocarditis
1st investigation
Other investigations
Heat stroke/insensible fluid losses
History
prolonged exposure to warm temperatures, prolonged exertion in hot climates, burns
Exam
dry skin and mucosa, loss of skin turgor, may be lethargic and confused, burns
1st investigation
- trial of fluids (oral or intravenous):
clinical improvement with rehydration
- serum chemistries:
increased BUN/creatinine ratio
Other investigations
Tension pneumothorax
History
sudden onset, often pleuritic, chest pain; shortness of breath; rapid deterioration; recent placement of a central venous pressure line; history of emphysema; chest trauma
Exam
absent unilateral breath sounds on the affected side; trachea deviated to the opposite side; hyper-resonance to percussion on affected side
1st investigation
- diagnostic and therapeutic needle thoracostomy:
hiss of air as catheter/needle enters the pleural space
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Other investigations
- bedside ultrasound:
pneumothorax visualized
- chest x-ray after decompression:
chest drain correctly placed; lung inflated
Cardiac tamponade
History
recent cardiac surgery or angiogram/angioplasty; chest trauma; malignancy; pericarditis; increasing shortness of breath on minimal exertion
Exam
muffled hearts sounds, low BP; jugular venous distention (Beck triad); pulsus paradoxus
1st investigation
- echocardiography:
pericardial fluid causing restriction of cardiac filling
- ECG:
electrical alternans
Other investigations
Neurogenic shock
History
brain or spinal cord injury, epidural or spinal procedures
Exam
hypotension, bradycardia, and hypothermia; warm dry peripheries with bounding pulses; priapism; flaccid paralysis of limbs
1st investigation
- MRI of the spine:
damage or compression of spinal cord
Other investigations
Adrenal crisis
History
can occur in context of other illness especially sepsis, trauma, and surgery, use of steroids either oral, inhaled, or topical over large areas; anticoagulant therapy; nausea and vomiting
Exam
lack of signs to indicate an alternative cause
1st investigation
- serum chemistry:
may be hyponatremic and hyperkalemic
- cortisol:
<20 micrograms/dL
Other investigations
- short synacthen test:
cortisol levels do not rise
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Thiamine deficiency
History
alcoholism, long-term nutritional deficiencies
Exam
warm bounding pulses, sometimes associated with skin changes, e.g., liver spots and brown patches
1st investigation
- thiamine level:
very low according to local lab parameters
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Other investigations
- CBC:
macrocytosis, anemia
Arteriovenous fistulae
History
depends on site of fistula, trauma especially gunshot wounds, recent instrumentation; e.g., central line, renal access procedure
Exam
signs of high-output heart failure, bounding pulses, low diastolic BP, high pulse pressure
1st investigation
- Doppler ultrasound:
demonstration of flow from artery to vein
Other investigations
- echocardiography:
bubbles appear on the left side of the heart after 3-5 cardiac cycles
- CT angiography:
anatomic demonstration of the fistula
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