Day #86 - "Demand Ischemia"

Today we talked about a great case of crescendo angina and NSTEMI occurring in the context of the physiological stress of severe anemia.

The discussant reviewed a good approach to the history of chest pain:

• Character, quality, radiation, intensity -- does this sound like typical, atypical or non-cardiac chest pain? Does this sound like another diagnosis?
  
• Associated symptoms: diaphoresis, nausea, vomiting, shortness of breath, palpitations, presyncope/syncope, orthopnea, PND
• Aggravating/alleviating factors -- rest, nitroglycerin, change in position, etc.

"Demand Ischemia" is a term that I have grown to dislike. Yes, it implies that the primary pathology is not ST elevation myocardial infarction or acute plaque rupture without ST-elevation. But it still indicates myocardial damage. And this was in a patient with known coronary artery disease.

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This patient had a macrocytic anemia as the precipitant.

Approach to macrocytic anemia:

• Problems with red blood cell production:
  
  • B12/folate deficiency (megaloblastic anemia)
    
  • Folate antagonists (i.e. methotrexate, TMP/SMX, AZT, hyrdroxyurea)
  • Alcoholism
  • Myelodysplastic syndrome
  • Multiple myeloma
    
  • Hypothyroidism
  • Liver disease (with target cells)
  • Hyperlipidemia (abnormal membranes lead to increased MCV)
• Destruction of red blood cells (or red blood cell loss)
  
  • Reticulocytosis (including "Runner's Anemia")
    
  • Congenital RBC defects like hereditary spherocytosis
    

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B12/folate deficiency (as a cause of anemia):

• Very unlikely if MCV less than 80
  
• Folate: Serum less than 4.5nM/L diagnostic if not anorexic or fasting, otherwise need to measure RBC folate
• B12: contraversy exists as to what is normal --
  
  • >221pmol/L unlikely deficient (high sensitivity)
    
  • 148-241pmol/L possible (borderline)
    
  • less than 148 (highly likely)
    
  • If borderline/possible and wish to confirm:
    
    • Homocysteine: Elevated in folate and B12 deficiency
      
    • Urine Methyl-Melonic Acid (MMA): Elevated in B12 deficiency
    • If both normal deficiency is ruled out, if elevated 99% specific
  • Diagnosis of pernicious anemia --> measure anti-intrinsic-factor antibodies, if present than Addison's pernicious anemia is confirmed.

A great MRI of B12 deficiency and neurologic sequelae is here.