A patient status-post surgery is often unable to eat due to nausea. A diabetic patient is likely to be suffering from hypoglycemia because of this; confusion, disorientation, and shakiness are common manifestations of hypoglycemia as well. Hyperglycemia may present with blurry vision, frequent urination, headaches, and fatigue. Diabetic ketoacidosis can manifest with thirst, frequent urination, weakness, and fruity-scented breath and occurs in patients with diabetes mellitus (DM) type 1. Diabetic hyperglycemic hyperosmolar syndrome may also present with the same symptoms of diabetic ketoacidosis but occurs in patients with DM type 2. Insulin resistance syndrome (also known as metabolic syndrome or prediabetes) usually does not present with manifestations, but people with severe insulin resistance syndrome may present with dark patches of skin on the back of the neck, elbows, knees, and/or armpits.

This patient's constellation of symptoms is most consistent with hypothyroidism. 

In hypothyroidism, which may occur for a handful of reasons, the patient typically does not produce significant levels of thyroid hormone (T3/T4), and therefore, a variety of functions that are modulated by thyroid hormone are impaired. Common symptoms associated with hypothyroidism are weight gain, lethargy, hair loss/brittle hair, dry skin, constipation, depression, cold sensitivity, bradycardia, and brittle nails, among other symptoms. On exam, the patient's thyroid may feel enlarged. Characteristic lab findings would be an elevated TSH level with low or low/normal T3/T4 levels. 

The other choices are incorrect for the following reasons:

1) Hyperthyroidism would be characterized by opposite symptoms from those seen in this patients. Patients with hyperthyroidism would be tachycardic, anxious, have poor heat tolerance, diaphoretic, may have diarrhea, and weight loss among, other symptoms. 

2) Thyroid storm is a severe, life-threatening condition that is essentially an acute, severe manifestation of excess levels of thyroid hormone (also known as thyrotoxicosis), and presents with very pronounced, severe signs of hyperthyroidism.

3) Diabetic ketoacidosis is almost exclusively seen in patients with diabetes (which is not noted in this patient) and often presents with diffuse abdominal pain, rapid shallow breathing, altered mental status, and a fruity odor on the breath.

4) Diabetes insipidus would present with increased frequency of urination of dilute urine, fatigue, enuresis, dehydration, and/or electrolyte abnormalities. 

The most likely diagnosis in this patient is Graves' Disease, which is a form of hyperthyroidism. 

Graves' Disease is an autoimmune condition in which the patient produces autoantibodies to the thyrotropin receptor, which overstimulates the release of T4 and T3, resulting in hyperthyroidism and its associated clinical manifestations (anxiety, palpitations, weight loss, diaphoresis, diarrhea, tremors, etc...). Further, in Graves' Disease, patients may have exophthalmos and/or lid lag, which are findings that are more specific to Graves' Disease than other causes of hyperthyroidism. This patient's constellation of symptoms is highly consistent with Graves' Disease. 

Hypothyroidism is not correct, as this patient is experiencing symptoms opposite those of hypothyroidism. In hypothyroidism, one would expect the patient to feel lethargic, weak, experience weight gain, dry skin, constipation, and potentially have depression.

Diabetes insipidus would present with increased frequency of urination of dilute urine, fatigue, enuresis, dehydration, and/or electrolyte abnormalities. 

Diabetes mellitus would not likely present in this manner. Patients are often asymptomatic at the time of diagnosis, and it would be discovered by elevated glucose or HbA1c readings on routine laboratory work. Occasionally, increased urinary frequency and dehydration, or more severe manifestations like hyperglycemic hyperosmolar nonketotic coma (HHNK) or diabetic ketoacidosis (DKA) would be a presenting scenario. 

A glucagonoma would present with necrolytic migratory erythema, most commonly, as well as severely elevated glucose concentrations.

The correct answer is "Adrenal insufficiency." This answer is correct because in this patient's case, he had been on a prolonged course of a high dose of prednisone, a corticosteroid. When patients are on prolonged courses, and/or high doses of corticosteroids, this can cause a negative feedback cycle on the body's own intrinsic production of corticosteroids. As a result, high doses of exogenous corticosteroids, or prolonged courses of any dose of exogenous steroids should not be abruptly stopped, as the body's own intrinsic steroid production will not yet have recovered, and therefore, the patient will exhibit signs of adrenal insufficiency. In this patient's case, while the physician does not completely eliminate the patient's exogenous steroid dose, he tapers the dose way too abruptly, from 40 mg to 5 mg, which dose not allow the body's own corticosteroid production to recover in time to meet the body's needs. Thus, the patient exhibits signs of adrenal insufficiency including lethargy, hypotension, hypoglycemia, and hyponatremia. 

Hyperaldosteronism and Conn's Syndrome (primary hyperaldosteronism) are incorrect as these are the opposite of what is observed in this patient. In a patient with hyperaldosteronism, the patient would likely be anxious and/or have high energy, would be hypertensive, and hypernatremic, as the sodium/potassium ATPase's activity would be upregulated in the setting of excess aldosterone.

Exogenous testosterone use would likely also cause increased anxiety/energy and hypertension, rather than lethargy and hypotension, as in this patient.

Surreptitious insulin use could explain lethargy, hypotension, and hypoglycemia, but would likely cause hypernatremia rather than hyponatremia, as insulin upregulates the activity of the sodium/potassium ATPase, which would increase rather than decrease serum sodium.

Conn syndrome (primary hyperaldosteronism) is hypertension due to elevated levels of aldosterone. High aldosterone causes excretion of potassium and retention of sodium, which leads to water retention and increase in blood pressure. While elevated levels of vasopressin (antidiuretic hormone) would also cause hypertension, Conn syndrome refers to the hypersecretion of aldosterone.

All of these symptoms are associated with a higher risk of developing diabetes. Turner syndrome is also know as XO, where the individual is a female, and is monosomic for the X-chromosome. Individuals with Turner syndrome are also at higher risk of heart disease, and hypothyroidism, and they are sterile. Down's syndrome is caused by trisomy of chromosome 21, and involves elevated risks for mental impairment, heart disease, and certain cancers. Kleinfelter's syndrome patients have the XXY-chromosomal expression. They are at a higher risk than the classically male or female public for osteoporosis, hypogonadism, and cardiovascular disorders.

80% of cases of Cushing's disease are caused by adrenocorticotropic hormone (ACTH)-secreting adenomas of the anterior pituitary. High ACTH ends up causes adrenal hyperplasia, which leads to secretion of extra cortisol. Corticosteroid use is the leading cause of Cushing syndrome, rather than Cushing's disease.

Insulin activates sodium-potassium ATPase in skeletal muscle cells causing an influx of potassium. Under certain circumstances, an incorrectly administered injection of insulin may kill patients due to its ability to acutely suppress plasma potassium concentrations.

GLUT-2 is the primary carrier for glucose transport into pancreatic beta cells. It does not depend on insulin to function. It thus aids the pancreatic beta cells sense glucose levels in the blood, which are then triggered to release insulin. GLUT-4 is active primarily in adipose and muscle tissue. 

The first onset of diabetes is generally marked by the following three signs: polyuria - frequent urination, polydypsia - increased thirst & fluid intake, and polyphagia - increased appetite. In children with type 1 diabetes, enuresis (involuntary urination) is often the first sign noticed by parents, along with unexplained weight loss and recurrent infections.