Atrophy

Atrophy Definition

Atrophy is a term that describes the wasting away of cell tissue. On a larger scale, atrophy can see a reduction in the size and function of a muscle or limb. This process if often gradual and chronic, if not permanent. However, atrophy is not exclusively a pathologic state. Atrophy is actually a part of our natural, homeostatic development. The wrinkles that appear on our faces as we age is atrophy, as is our thinning hair and the loss of teeth. There are many reasons for why a tissue may atrophy. It can be caused by age or genetics, such as inheriting a faulty set of genes that signal cell lysing or inhibit a crucial protein from assembling. Another factor is environmental change. Depending on our health or income status, we may experience nutritional deficits. Or a physical injury may pierce our tissues or damage the nerves innervating our muscles. Likewise, chronic illness can impact our tissues permanently.

The inevitable consequence of tissue atrophy is that it diminishes the impacted limb’s ability to perform its functions. However, the actual degree of damage depends on its partial or complete effect and on the subject of atrophy. Atrophy that targets nerves or a wide-spread muscle will systemically affect the body. This kind of effect would result in pronounced deficits (i.e. multiple sclerosis). In fact, sufferers of atrophy often show two clinical signs: shortened limbs and bodily weakness.

Atrophy Types

While atrophy can describe a wide array of conditions, it can arise either naturally or from disease. In fact, some presentations can occur for either reason. For example, Disuse atrophy is a progressive withering of bone and muscle that results from prolonged inactivity. In the event that a patient develops a chronic illness like cancer or HIV, bone density and muscle mass whittle down considerably. Cachexia is a clinical name for a non-intentional muscle loss that follows illness or precedes death. Hence, it’s colloquial name, “muscle wasting.” The same applies to bed-ridden patients with spinal injuries, paraplegia, or sudden disabilities. However, disuse atrophy can also take place in healthy individuals. For instance, a student athlete may experience some disuse atrophy during their off-season from the sport they play in face of a reduced work load.

Symptoms of muscle wasting?

• General or localized weakness


• Limb numbness


• Ataxia


• Pain


• Muscle spasms


• Unintentional weight loss

Pathologic atrophy presents itself in many areas of the body for varied reasons. We will go more in depth into common presentations, but it is notable to mention that not all atrophy affects muscle. Atrophy can target connective tissue fibers, such as tendon, bone, ligaments, and fat tissue. Neural diseases (like multiple sclerosis or Parkinson’s) atrophies brain tissue and neural cells, or severs the connections within. Glandular atrophy can occur with long-term hormonal or steroid excess, or nutritional imbalance. Atrophy, then, is quite involved and relies on an interplay of signaling events that continue to be understood.

Muscle Atrophy

Muscle atrophy typically refers to the weakening of skeletal muscles. These are the muscles that form the framework that moves our limbs. They are also called striated muscles that carry out voluntary movement. There are generally two types of muscular atrophy: disuse and neurogenic atrophy. Disuse atrophy results from muscle inactivity, as discussed before. When muscles themselves are not used enough by a patient who is weak, bed-ridden, or paralyzed, the inactive muscles will whittle down with lack of use. This results in a gradual decline in the total muscle mass. However, disuse atrophy can also benefit from physical therapy. In some instances, exercise of the affected muscles can reverse atrophy completely and better nutrition can aid in the body’s recovery.

Neurogenic atrophy, on the other hand, is a more severe type. Unlike disuse atrophy, neurogenic atrophy will affect the nerves connected to the muscles rather than the muscles themselves. Nerve damage is much harder to treat and will not reverse with exercise. Common causes of nerve damage include alcohol abuse, toxins, and injury. Other examples of diseases that affect the nerves that engage muscle movement are ALS, Polio, carpal tunnel syndrome and spinal cord injury. Diagnosis of muscle atrophy typically occurs at a doctor’s clinic, and includes measuring the muscle size of the affected limb, and taking blood tests, MRI, and nerve studies.

Spinal Muscular Atrophy

Spinal muscular atrophy, or SMA, is an autosomal recessive spinal disorder that is carried by 1 in 40 people. SMA specifically atrophies motor neuron cells in the spinal cord. Our spinal cords are rich in nerve cells that help coordinate our body’s movement. In fact, the majority of the neurons that control our muscles can be found within our spinal cord. But of course, the atrophy eventually affects muscles, as they whittle down in response to not receiving signals from the damaged nerves and are therefore inactive.

Since no two SMA sufferers share the same exact experience with how their disease progresses, SMA is subtyped into four categories.

SMA Types:

1. Type I: the most common and severe type of SMA that is usually diagnosed before an infant turns 6 months old.


2. Type II: is diagnosed between the ages of 6 months and 2 years old. It is often first noticed if an infant displays a motor delay or fails to meet these milestones (i.e. the baby may be able to sit up without assistance, but will need help sitting back down. The infant will not be able to walk and will require a wheelchair.)


3. Type III: also nicknamed juvenile SMA, is diagnosed between 18 months and 3 years of age, or as late as in the teens. Patients will progressively lose mobility until they need a wheelchair.


4. Type IV: is a very rare type that surfaces in adulthood. Thus, it’s said to have an adult-age onset that will lead to mild motor issues. The age of onset is typically between age 18 and 35.

Vaginal Atrophy

Vaginal atrophy is a disorder that attacks the muscle lining of the vagina and urinary tract. Common symptoms include vaginal soreness and painful intercourse. Low levels of estrogen are to blame for vaginal atrophy. Estrogen loss occurs during peri- or post-menopause, but also during breastfeeding in new mothers. An artificial way that estrogen levels may diminish is with long-term of medication that treats estrogen conditions like endometriosis. Though taboo surrounding vaginal disease prevents many women from treating their symptoms, vaginal atrophy can be ameliorated with vaginally administered estrogen creams and lubricant.

Quiz

1. Which of the following is the atrophy type that gives rise to disease by affecting the nerves connected to muscle tissue?
A. Disuse atrophy
B. Seize atrophy
C. Glandular atrophy
D. Neurogenic atrophy

Answer to Question #1

D is correct. Neurogenic atrophy is the most severe form of muscular atrophy as it injures the nerve that innervates the muscle and can result from any nerve damage caused by injury or toxins, etc.

2. Which cell type does SMA atrophy?
A. Glial cells
B. Motor neurons
C. Interneurons
D. Schwann cells

Answer to Question #2

B is correct. SMA specifically targets motor neurons in the spinal cord. Motor neurons are those that innervate the muscles involved in movement.

3. Which type of SMA has an adult age onset?
A. Type I
B. Type II
C. Types III
D. Type IV

Answer to Question #3

D is correct. SMA is divided into subtypes to account for the fact that no two people experience their illness in the same way, and the progression of the disease varies. Type IV, specifically, surfaces after the age of 18 and leads to mild disability.

References

• Cure SMA (2017). “Types of SMA.” Cure SMA Org. Retrieved on 2017-06-07 from http://www.curesma.org/sma/about-sma/types-of-sma/?referrer=https://www.google.com/?referrer=http://www.curesma.org/sma/about-sma/types-of-sma/


• MDA (2017). “Spinal Muscular Atrophy: What is spinal muscular atrophy.” MDA for strength, independence, and life. Retrieved on 2017-06-08 from https://www.mda.org/disease/spinal-muscular-atrophy


• MDA (2014). “Spinal Muscular Atrophy: An Overview.” Muscular Dystrophy Australia Retrieved on 2017-06-07 from http://old.mda.org.au/Disorders/Atrophies/SMA.asp


• Medline Plus (2017). “Muscle Atrophy.” Medline Plus: US National Library of Medicine. Retrieved 2017-06-07 from https://medlineplus.gov/ency/article/003188.htm


• Mac Bride, M et al (2010). “Vulvovaginal Atrophy.” Mayo Clin Proc. 85(1): 87-94.

Atrophy