EDEMA OF THE EXTREMITIES

Edema of the extremities is a common symptom. Most physicians, therefore, have an immediate working diagnosis when the patient walks into the office: Congestive heart failure (CHF) if the edema is bilateral and deep vein phlebitis if it is unilateral. Many times this is right. However, what if the heart and chest sound normal and there is a negative Homan sign? Obviously, before the physician questions the patient the clinician needs a more complete list of diagnostic possibilities. Physiology is the key to that list. Fluid is passing from the blood compartment into the subcutaneous tissues and back again all the time. Why does it stay in the subcutaneous tissues? There are four main physiologic reasons and three minor ones.

1. The pressure in the veins may be so high that it overcomes the oncotic pressure of the albumin and other proteins in the blood. This is the explanation in phlebitis, venous thrombosis, pelvic tumors, and right-sided CHF (partially).

   ---

   PHYSIOLOGIC MECHANISMS OF EDEMA

   					Abnormal
   	Increased	Increased	Decreased		Protein in	Loss of
   	Venous	Arterial	Serum	Lymphatic	Subcutaneous	Tissue
   	Pressure	Pressure	Albumin	Obstruction	Tissue	Turgor	Aldosteronism
   Congestive Heart Failure	√		√				√
   Nephrosis			√				√
   Cirrhosis	√		√				√
   Pelvic Tumor	√
   Thrombophlebitis	√
   Filariasis				√
   Hypothyroidism					√
   Beriberi			√			√
   Malignant Hypertension		√					√
   Acute Glomerulonephritis		√					√
   Toxemia of Pregnancy		√	√				√

   ---

2. The pressure in the arteries may be so high that more fluid is pushed out than can be reabsorbed with normal oncotic pressure. This may be the case in acute glomerulonephritis and malignant hypertension.
3. The level of serum albumin may be so low that the oncotic pressure drops to a point where it cannot reabsorb all the fluid being driven out by the forward pressure of the arteries or backward pressure of the veins. This is seen in conditions in which either too little albumin is produced (cirrhosis of the liver) or too much albumin is lost in the urine (nephrotic syndrome of diabetes mellitus, lupus erythematosus, amyloidosis, and several other disorders of the kidney). It is also probably a component of the edema in beriberi and CHF.
4. The lymphatic channels that pick up any excess fluid that the veins cannot pick up may be blocked. This occurs notably in filariasis, Milroy disease, and lymphedema following mastectomy, but other conditions may also block the lymphatics.
5. An abnormal protein (mucoprotein) may be deposited in the tissues and lead to edema. This results in the nonpitting edema of hypothyroidism (myxedema).
6. A reduction in tissue turgor pressure may be responsible for the edema in older people and beriberi (vitamin B₁ deficiency).
7. Retention of salt as in primary and secondary aldosteronism is a minor factor, because most cases of aldosterone-secreting adenomas do not have significant edema.

It would be a serious omission not to mention local conditions such as cellulitis, burns (especially sunburn), contusions, and urticaria that may cause edema, but these are usually obvious. Edema is classified according to the anatomic site of origin and the mechanisms that are responsible in Table 26.

Approach to the Diagnosis

Bilateral pitting edema of the lower extremities is usually due to CHF, nephrosis, or cirrhosis of the liver. Venous pressure and circulation time will rule out CHF, but echocardiography can be more definitive. Serum and urine osmolality can be helpful also. If there is nephrosis, there will be significant lowering of the serum albumin level and proteinuria. Liver function studies will usually confirm cirrhosis or liver disease, but ultrasonography can reveal ascites to assist in the diagnosis. Nonpitting edema of the lower extremities will usually be due to lymphatic obstruction, but hypothyroidism can be ruled out with a free thyroxine (T₄) or thyroid-stimulating hormone (TSH) assay. Unilateral edema of the lower extremities suggests deep vein thrombosis, which can be confirmed by Doppler ultrasound studies, plethysomography, or contrast venography. A CT scan of the chest will help diagnose constrictive pericarditis, which is rarely found today. Spirometry and arterial blood gas analysis will diagnose pulmonary emphysema with cor pulmonale.

Other Useful Tests

1. Complete blood count (CBC) (anemia)
2. Chemistry panel (nephrosis, cirrhosis)
3. Renal function test (nephritis, nephrosis)
4. Antinuclear antibody (ANA) analysis (collagen disease)
5. CT scan of the abdomen and pelvis (ovarian cyst or tumor)
6. Lymphangiogram (lymphedema)
7. CT scan of the chest (superior vena cava syndrome)
8. Serum protein electrophoresis (collagen disease, multiple myeloma)

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Book Source Details

• Book Title: Differential Diagnosis in Primary Care
• Author(s): R. Douglas Collins MD, FACP
• Year of Publication: 2007
• Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.

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More About This Book: Title: Differential Diagnosis in Primary Care Authors: R. Douglas Collins MD, FACP Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 0-7817-6812-8

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