Is It All In My Head?

So the good news is....the muscle and joint pain I feel is not caused by my joints degenerating. I was getting quite concerned that Femara, which keeps my body from producing estrogen, was having a degenerative effect.

My ankles, knees and hips ache. This is not new. For a while now, however, I've felt that my knee joints were slipping when I am out running. Do you know the slipping feeling? You get a sharp pain below the kneecap and then the knee sort of collapses and you have to catch yourself. My mind associates lasting new abnormal aches and pains, that occur more than they used to, to the effects of Femara.

So I submitted another question to the University of Montana Drug Information Service. I wanted to know if my joint pain, stiffness and slipping weirdness was going to progressively get worse. I wanted to know if it was caused by Femara. My fear was that I wouldn't be able to run at some point. Below is their response.

Thank you for your question regarding Femara and muscle or joint deterioration.

Femara (letrozole) is an aromatase inhibitor that is used in the adjuvant treatment of breast cancer and the prevention of its recurrence. It blocks the action of the aromatase enzyme, which converts androgens to estrogens. Letrozole causes the near complete inhibition of the aromatase enzyme, which will results in a considerable depletion of estrogen levels after two to four days of therapy. This results in the starvation of estrogen-sensitive cancer cells. There have been no published reports of letrozole causing muscle or joint deterioration, but it has been reported to cause musculoskeletal pain, with a 22% incidence of arthralgia and bone pain, 18% incidence of back pain, 10% incidence of limb pain, and a 7% incidence of arthritis and myalgia. The exact cause of musculoskeletal pain is unclear, but the estrogen deprivation associated wtih aromatase inhibitor therapy may provide some explanation.

Estrogen may have an effect on how a person responds to pain. It has been shown that estrogen seems to have an anti-inflammatory effect on tissues in the body, which has been illustrated by the improvement of rheumatoid arthritis, multiple sclerosis and inflammatory bowel disease in women who are pregnant and therefore have higher estrogen levels. Studies suggest that high levels of estrogen may help reduce pain by causing the release of endorphins and enkephalins in the receptors that reduce pain sensitivity in the body. Neurons in the brain and spinal cord that contain opioid receptors may have estrogen receptors that reduce pain sensitivity in the presence of estrogen. When estrogen levels decrease, the ability to reduce pain is diminished. Estrogen deficiency can also cause loss of bone mineral density, which may also contribute to arthralgias.


Aromatase inhibitors such as letrozole, can cause musculoskeletal pain. The exact mechanism is unknown, but there have been no published reports indicating the pain is due to joint or muscle deterioration. The current hypothesis is that the estrogen deficiency caused by aromatase inhibitors may be responsible for increasing the body's sensivity to pain.

There you have it! The pain is in my head (my brain to be exact)! I feel pain more clearly now because I don't have estrogen to block my brain from perceiving it. Thats all. This makes me feel much better about my future. I can handle the pain. Anyone who exercises knows that pain from working your body can feel good. You know you have "damaged" your muscles enough that they will rebuild stronger.

Now when I wake in the morning and hobble to the bathroom I will remember that my joints are fine. I am just feeling more than I used to.

Here's John and I out on a hike a few weeks ago. Check out my hair 3 months post chemo!