The correct answer is bulimia nervosa. 

Bulimia nervosa is an eating disorder in which a patient classically consumes large amounts of food (binge eating) and then induces vomiting (purge behavior) to expel the food prior to absorption in the gastrointestinal tract. As such, the patient restricts their ability to gain weight. Patients with bulimia nervosa are frequently successful, high-achieving individuals under a great deal of stress, and often may be adolescent athletes, as patients in this population frequently have specific weight cutoffs that they must achieve for their respective sports/activities. Some signs of bulimia nervosa, as exhibited by this patient, are thin, brittle hair, a hypovolemic appearance (due to frequent vomiting), excoriations on the knuckles (from self-inducing vomiting with their hands), yellow discoloration of the teeth (from the acidity of vomitus), and swelling of the parotid glands (colloquially known as "chipmunk cheeks") as a response to the frequent vomiting. Patients with bulimia may also use other methods to purge themselves of food and drinks including diuretic use, and/or laxative use. 

A key distinction between bulimia nervosa and anorexia nervosa is that in bulimia the patient exhibits a form of purge behavior following binge eating, whereas in anorexia, classically, the patient simply restricts eating rather than binging and purging. 

Hypothyroidism is not a correct answer choice because while this patient is exhibiting lethargy, weakness, and brittle hair, given the constellation of her other symptoms and exam findings, it is less consistent with her presentation than bulimia nervosa. If these symptoms persisted following treatment for bulimia, then hypothyroidism could be considered as a concurrent finding.

Exogenous use of testosterone would not account for the symptoms seen in this patient.

Marfan's syndrome would also not account for the symptoms seen in this patient.

The hippocampus is implicated in memory formation and processing. As individual's age, the development of plaques in this area of the brain lead to the pathogenesis of Alzheimer's dementia. The amygdala is the brain structure associated with fear. Wernicke's area is for language formation. The occipital lobe deals with vision. The prefrontal cortex is involved with primative behavior and impulses.

While any of this patient's symptoms may be present in multiple sclerosis, this specific set of symptoms is typical of cauda equina syndrome. This is a condition in which trauma or impingement within of the spinal canal compresses the cauda equina, the bundle of spinal nerves and nerve roots near the base of the spinal cord. 

Neither prostatitis or Parkinson's disease generally present with this distinct triad of back pain, saddle anesthesia, and sexual and/or urinary dysfunction.

A seizure is an abnormal electrical event in the brain, usually caused by diffuse, rapid firing of neurons within the brain. An EEG is the diagnostic test used to capture events and identify where in the brain the impulse is generated from. EEG consists of electrodes placed on the scalp. The other tests mentioned cannot identify the electrical activity of the brain.

The correct answer is "benzodiazepine withdrawal" because the patient's presentation, with agitation, confusion, and panic, coupled with his physical and vital sign findings (tachycardia, hypertension, profuse sweating), and historical information (has not taken a regular medication of his for 24 hours) are all consistent with benzodiazepine withdrawal. Benzodiazepines are a class of medications that have anxiolytic and anticonvulsant properties, as they increase the efficacy of the neurotransmitter GABA. Given their anxiolytic properties, and in some types, their rapid speed of onset, they are a commonly abused class of drugs. 

Benzodiazepine withdrawal occurs when a patient who regularly takes benzodiazepine medications and has a physiological dependence abruptly stops taking these medications. Symptoms of benzodiazepine withdrawal include but are not limited to anxiety, panic, agitation, hypertension, tachycardia, diaphoresis, and inability to sleep. If untreated, this can lead to seizures and worsening confusion. As such, it is important to recognize these symptoms early and restart benzodiazepine treatment as early as possible in these patients.

Benzodiazepine intoxication, cocaine withdrawal, and heroin intoxication are incorrect as the patient would exhibit symptoms opposite those described in this example.

Ketamine intoxication is incorrect, as ketamine is a dissociative medication that would not likely cause this constellation of symptoms, and would be more likely to present with dissociative properties.

The correct answer is "trichotillomania." This is the correct answer, as this term describes the obsessive-compulsive condition in which patients have an uncontrollable urge to remove their hair, which causes baldness, and social/emotional distress and impairment. Patients typically pull hair from the scalp, eyebrows, lashes, and extremities. Treatment includes a variable combination of psychotherapy and/or medications.

On the other hand, the other choices are incorrect. Walking-corpse syndrome is a psychiatric condition in which a patient thinks that they are dead, while in reality, they are indeed alive. Arachnophobia is a fear of spiders. Agoraphobia is a fear of being in public places. Last, social phobia is a fear of social situations.

The "worst headache of my life" or "thunderclap headache" is characteristic of subarachnoid hemorrhage. This is bleeding in the brain and must be treated urgently. It is usually caused by the rupture of a berry aneurysm within the blood supply to the brain. Hypertension is a major risk factor.

Multiple sclerosis is an autoimmune process with no exact known cause. The myelin sheath is attacked and plaque formation occurs in various regions of the CNS. Without myelin, nerve conduction slows down and may eventually be completely blocked leading to widespread loss of function. 

Loss of the dopamine-producing neurons describes Parkinson's disease. Excess dopamine describes dementia. Deficiency of acetylcholine describes Huntington's disease, and the autoimmune disease of the neuromuscular junction is known as Myasthenia Gravis.

Bell's palsy is due to dysfunction of cranial nerve VII, the facial nerve. The facial nerve provides motor control to the musculature of the face and sensory innervation of taste, facial sensation, and parasympathetic innervation of the submandibular and sublingual glands. 

Migraine headaches are commonly treated at first by over the counter (OTC) medications such as NSAIDS and acetaminophen. Other treatment options include triptans, antidepressants such as amitriptyline, and anti-hypertensives (beta blockers and calcium channel blockers).