USMLE® Step 1 style questions USMLE
A 55-year-old woman comes to the office because of swelling in her left arm for the past 6 months. Her medical history includes a mastectomy with axillary node dissection for breast cancer a year ago, and an infection in her left arm 2 months ago. Her temperature is 36.5°C (97.7°F), pulse is 72/min, respirations are 14/min, and blood pressure is 110/68 mm Hg. Examination shows firm skin over the left arm with soft underlying tissue. The arm is not painful or discolored. Which of the following is the most likely diagnosis?
Lymph is the fluid circulating in the lymphatic system, and edema refers to fluid buildup in the body’s tissues; therefore, lymphedema is a buildup of lymph somewhere in the body’s tissues.Typically, this happens as a result of some obstruction in the lymphatic system.
All right, let’s back up and briefly talk about this lymph stuff. Oxygenated blood gets sent from the heart to your tissues via arteries, which get smaller and smaller until they feed the capillary beds. The capillary beds then provide nutrients to your cells and pick up waste. Now, deoxygenated blood then feeds back into larger and larger veins, and goes back to the heart. Pressure on the arterial side is a lot higher than on the venous side, so as blood comes into the capillary bed from the smaller arteries, called arterioles, the plasma — the colorless, fluid part of blood — is literally forced out into the interstitial space, or the space between cells. The majority of that fluid is reabsorbed on the venous side, but typically there’s more forced into the tissue through the arterial side than is taken out by the venous side.
Here’s where the lymphatic system comes into play. All of that excess fluid gets pulled into the afferent lymphatic capillaries, which are closed-ended vessels found throughout the body, including, scientists discovered in 2015, in the brain. These lymphatic capillaries have larger openings than the venous capillaries, which means that in addition to the interstitial fluid, they can accept larger proteins, cellular debris, and even bacteria, which get squeezed out of the arterial side, but are too large to get back into the venous capillaries. Once all of that stuff is in the lymphatic system, it’s called lymph. Also, those afferent lymphatic vessels have one-way valves that, along with smooth muscle contraction, keep the lymph moving along toward the lymph nodes, which have immune cells that once again help filter the fluid, getting rid of potential microbial threats. The fluid then leaves the lymph nodes and drains back into the systemic veins via the thoracic duct, or left thoracic duct, which empties into the left subclavian and jugular veins, and right thoracic duct, which empties into the right subclavian and internal jugular veins, to rejoin the blood once again.
So, let’s get back to lymphedema. When something blocks the normal flow in the lymphatic system, the lymph gets backed up, which means the interstitial fluid can’t drain properly, causing fluid to accumulate in the interstitial space. This means that those proteins and cellular debris build up too, right? When all that stuff stagnates, it initiates an inflammatory reaction that causes macrophages to release inflammatory molecules, which ultimately damage surrounding cells. This leads to fibrosis, which is the thickening of connective tissue, or the creation of scar tissue. Fibrosis causes hardening of the affected area, which is commonly in the limbs.
One of the most common global causes of lymphedema is filariasis, an infection with nematode parasites, which are tiny worms; the most common species are: Wuchereria bancrofti, Brugia malayi, and Brugia timori. Filariasis happens when one of these nematodes gets in the lymphatic system and causes a bit of fibrosis, which creates a physical blockage that obstructs the normal flow of lymph. In developed nations, lymphedema is most commonly caused by cancer malignancy and/or its treatment.
Cancer-associated causes causes of lymphedema include: the lymphatic system itself develops a cancer that causes an obstruction, which is called a primary lymphoma; it could be a result of metastatic tumor cells from somewhere else that travel to the lymphatic system and cause an obstruction; or, it could be the result of cancer treatment, such as if an affected lymph node or group of nodes are removed via surgery. The most common cancer-associated cause of lymphedema is removal of the lymph nodes as a treatment for breast cancer. You’ll notice that all of these causes of lymphedema are the result of some other disease, so these are situations that represent secondary lymphedema.