USMLE® Step 1 style questions USMLE
A 17-year-old girl is admitted to the hospital for nutritional support after her parents brought her to the hospital earlier today due to marked dehydration and weakness. The patient has a past medical history significant for anorexia nervosa which was being treated with psychotherapy. On admission, the patient’s temperature is 36.4°C (97.5°F), pulse is 52/min, and blood pressure is 84/62 mmHg. Body mass index is 15 kg/m2. Parenteral nutritional replenishment is started. On the second day of admission, the patient is experiencing severe myalgias, paresthesias, and shortness of breath. Physical examination reveals bibasilar crackles. Laboratory evaluation reveals markedly decreased serum potassium levels and phosphorus levels. Increased secretion of which of the following hormones is most likely the cause of this patient’s current clinical condition?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS
Anorexia nervosa, which is often just called anorexia, is a disorder characterized by very low weight (typically less than 85% of normal body weight), a constant fixation on avoiding putting on even the slightest amount of weight, and having a distorted view of one’s own body weight or shape, often believing that one is overweight, while actually being underweight.
There are two main types of anorexia. One form of the disorder is the restricting type, where people reduce the amount of food they eat in order to lose weight.
Another form of the disorder is the binge-and-purge type, where individuals eat large amounts of food in one sitting and then purge that food by vomiting or taking laxatives.
This second type can be confused with another eating disorder, bulimia nervosa, but the main distinction between these two disorders has to do with an individual’s weight.
Individuals with bulimia are usually normal weight or overweight, whereas individuals with anorexia are underweight.
Because of this, people can potentially start out with bulimia, and then develop anorexia over time.
Anorexia can be further split by levels of severity.
A body mass index (or BMI) between 18.5 and 24.9 is considered healthy.
People diagnosed with anorexia have a BMI below this threshold: a BMI between 17 and 18.5 is considered mildly anorexic, a BMI of 16-17 is considered moderately anorexic, a BMI of 15-16 is severely anorexic, and a BMI of less than 15 is considered extremely anorexic.
In addition to having a low BMI, individuals with anorexia are typically fearful of weight gain, and often have a psychological obsession with the caloric and fat content of food.
This leads to food-restrictive behaviors, purging, over-exercise, and frequent weight checks.
People with anorexia might perform specific food rituals, like cutting food into small pieces, or eating foods in a specific order.
They might refuse to ever eat in front of people, or cook elaborate meals for others, but then not eat themselves.
There is often a loss of muscle tissue throughout the body, reflected by a low creatinine level and symptoms of fatigue from weak muscles throughout the body, including a weak diaphragm which can cause difficulty breathing.
Even the heart can lose muscle, and this loss of cardiac muscle tissue can lead to bradycardia (less than 60 heart beats per minute) and hypotension (a blood pressure below 90/50), as well as orthostatic hypotension, which when blood pressure falls when a person stands up after lying down.
People with anorexia may also have serious electrolyte abnormalities like low potassium, magnesium, and phosphate levels, as well as key vitamin deficiencies, with lowered levels of thiamine (also known as Vitamin B1).
The bone marrow can start shutting down, leaving the body with fewer white blood cells, leading to a dampened immune response, fewer red blood cells, leading to lower energy levels, and fewer platelets, leading to easy bleeding and bruising.
Anorexia can also cause osteoporosis where the bones become weak and susceptible to fractures.
The skin can change, becoming dry and scaly.