The differential diagnoses of anorexia nervosa (AN) includes various types of medical and psychological conditions, which may be misdiagnosed as AN. In some cases, these conditions may be comorbid with AN because the misdiagnosis of AN is not uncommon. For example, a case of achalasia was misdiagnosed as AN and the patient spent two months confined to a psychiatric hospital. A reason for the differential diagnoses that surround AN arise mainly because, like other disorders, it is primarily, albeit defensively and adaptive for, the individual concerned.

Anorexia Nervosa is a psychological disorder characterized by extremely reduced intake of food. People suffering from Aneroxia Nervosa have a low self-image and consider themselves overweight.

Common behaviors and signs of someone suffering from AN:

- Forcing oneself to vigorously exercise even in adverse conditions or when their health does not permit it.

- Forcing own self to urinate and excrete waste product from the body.

- Using substituted amphetamines (stimulants that can reduce appetite) to reduce appetite.

- Skin turning yellow

Some of the differential or comorbid medical diagnoses may include:

- achalasia – There have been cases where achalasia, a disorder of the esophagus which affects peristalsis, has been misdiagnosed as AN. It has been reported in cases where there is sub-clinical manifestation of anorexia nervosa and also in cases where the full diagnostic criteria AN have been met.

- acute pandysautonomia is one form of an autonomic neuropathy, which is a collection of various syndromes and diseases which affect the autonomic neurons of the autonomic nervous system (ANS). Autonomic neuropathies may be the result of an inherited condition or they may be acquired due to various premorbid conditions such as diabetes and alcoholism, bacterial infection such as Lyme disease or a viral illness. Some of the symptoms of ANS which may be associated with an ED include nausea, dysphagia, constipation, pain in the salivary glands, early saiety. It also affects peristalsis in the stomach. Acute pandysautonomia may cause emotional instability and has been misdiagnosed as various psychiatric disorders including hysterical neurosis and anorexia nervosa.

- Lupus: various neuropsychiatric symptoms are associated with systemic lupus erythematosus (SLE), including depression. Anorexia and weight loss also may occur with SLE and while rare it may be misdiagnosed as AN.

- Lyme disease is known as the "great imitator", as it may present as a variety of psychiatric or neurologic disorders including anorexia nervosa. "A 12 year old boy with confirmed Lyme arthritis treated with oral antibiotics subsequently became depressed and anorectic. After being admitted to a psychiatric hospital with the diagnosis of anorexia nervosa, he was noted to have positive serologic tests for Borrelia burgdorferi. Treatment with a 14 day course of intravenous antibiotics led to a resolution of his depression and anorexia; this improvement was sustained on 3 year follow-up." Serologic testing can be helpful but should not be the sole basis for diagnosis. The Centers for Disease Control (CDC) issued a cautionary statement (MMWR 54;125) regarding the use of several commercial tests. Clinical diagnostic criteria have been issued by the CDC (CDC, MMWR 1997; 46: 531-535).

- Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare genetic disorder characterized by gastrointestinal dysmotility, severe cachexia progressive external ophthalmoplegia, post-prandial emesis (vomiting after eating), peripheral neuropathy, and diffuse leukoencephalopathy. Onset is prior to age 20 in 60% of cases. ""Miss A" was a 21-year-old Indian woman diagnosed as having treatment-resistant anorexia nervosa." It was subsequently proven to be MNGIE

- superior mesenteric artery syndrome (SMA syndrome) "is a gastrointestinal disorder characterized by the compression of the third or transverse portion of the duodenum against the aorta by the superior mesenteric artery resulting in chronic partial, incomplete, acute or intermittent duodenal obstruction". It may occur as a complication of AN or as a differential diagnosis. There have been reported cases of a tentative diagnosis of AN, where upon treatment for SMA syndrome the patient is asymptomatic.

- Addison's disease is a disorder of the adrenal cortex which results in decreased hormonal production. Addison's disease, even in subclinical form, may mimic many of the symptoms of anorexia nervosa.

- Brain tumors: There are multiple cases were the neuropsychiatric symptoms of a brain tumor were attributed to AN, resulting in misdiagnosis. The tumors in these cases were noted in various regions of the brain including the medulla oblongata, hypothalamus, pituitary gland, pineal gland and the obex.

- Simmond's disease (organic hypopituitarism) – "A 20-year-old Japanese man with a hypothalamic tumor which caused hypopituitarism and diabetes insipidus was mistakenly diagnosed as anorexia nervosa because of anorexia, weight loss, denial of being ill, changes in personality, and abnormal behavior resembling the clinical characteristics of anorexia nervosa"

- Brain calcification either dystrophic calcification or metastatic calcification can present with neuropsychiatric symptoms including those associated with AN and comorbid disorders such as obsessive compulsive disorder.

- cysts that occur in the central nervous system such as dermoid cysts and arachnoid cysts can cause neuropsychiatric symptoms including psychosis.

- Celiac disease is an inflammatory disorder triggered by peptides from wheat and similar grains which cause an immune reaction in the small intestine. "information on the role of the gastrointestinal system in causing or mimicking eating disorders is scarce."(Leffler DA "et al.")

- Gall bladder disease which may be caused by inflammation, infection, gallstones, obstruction of the gallbladder or torsion of the gall bladder – Many of the symptoms of gall bladder disease may mimic anorexia nervosa (AN). Laura Daly, a woman from Missouri, suffered from an inherited disorder in which the gall bladder was not properly attached; the resultant complications led to multiple erroneous diagnoses of AN. Upon performance of a CCK test, standard imaging techniques are done with the patient lying prone, in this instance it was done with the patient in an upright position. The gall bladder was shown to be in an abnormal position having flipped over the liver. The gallbladder was removed and the patient has since recovered. The treatment was performed by William P. Smedley in Pennsylvania.

- colonic tuberculosis misdiagnosed as anorexia nervosa in a physician at the hospital where she worked – "This patient, who had severe wasting, was misdiagnosed as having anorexia nervosa despite the presence of other symptoms suggestive of an organic disease, namely, fever and diarrhea"(Madani, A 2002).

- Crohn's disease: "We report three cases of young 18 to 25 year-old girls, initially treated for anorexia nervosa in a psychiatric department. Diagnosis of Crohn's disease was made within 5 to 13 years."(Blanchet C, Luton JP. 2002)"This disease should be diagnostically excluded before accepting anorexia nervosa as final diagnosis". (Wellmann W "et al.")

- hypothyroidism, hyperthyroidism, hypoparathyroidism and hyperparathyroidism may mimic some of the symptoms of, can occur concurrently with, be masked by or exacerbate an eating disorder and/or various comorbid disorders such as anxiety and depression.

- Insulinomas are (pancreatic tumors) that cause an overproduction of insulin, causing hypoglycemia. Various neurological deficits have been ascribed to this condition including misdiagnosis as an eating disorder.

- Multiple sclerosis (encephalomyelitis disseminata) is a progressive autoimmune disorder in which the protective covering (myelin sheath) of nerve cells is damaged as a result of inflammation and resultant attack by the bodies own immune system. In its initial presentation, MS has been misdiagnosed as an eating disorder.

An inferiority complex is the lack of self-worth, a doubt and uncertainty about oneself, and feelings of not measuring up to standards. It is often subconscious, and is thought to drive afflicted individuals to overcompensate, resulting either in spectacular achievement or extremely asocial behavior. In modern literature, the preferred terminology is "lack of covert self-esteem". For many, it is developed through a combination of genetic personality characteristics and personal experiences.

Classical Adlerian psychology makes a distinction between primary and secondary inferiority feelings.

- A primary inferiority feeling is said to be rooted in the young child's original experience of weakness, helplessness and dependency. It can then be intensified by comparisons to siblings, romantic partners, and adults.

- A secondary inferiority feeling relates to an adult's experience of being unable to reach a subconscious, reassuring fictional final goal of subjective security and success to compensate for the inferiority feelings. The perceived distance from that reassuring goal would lead to a negative/depressed feeling that could then prompt the recall of the original inferiority feeling; this composite of inferiority feelings could be experienced as overwhelming. The reassuring goal invented to relieve the original, primary feeling of inferiority which actually causes the secondary feeling of inferiority is the "catch-22" of this dilemma, where the desperate attempt to obtain therapeutic reassurance and delivery from a depressing feeling of inferiority and worthlessness repeatedly fails. This vicious cycle is common in neurotic lifestyles.

The signs of carnitine-acylcarnitine translocase deficiency usually begin within the first few hours of life. Seizures, an irregular heartbeat, and breathing problems are often the first signs of this disorder. This disorder may also cause extremely low levels of ketones (products of fat breakdown that are used for energy) and low blood sugar (hypoglycemia). Together, these two signs are called hypoketotic hypoglycemia. Other signs that are often present include ammonia in the blood (hyperammonemia), an enlarged liver (hepatomegaly), heart abnormalities (cardiomyopathy), and muscle weakness. This disorder can cause sudden infant death.

A term whose meaning is synonymous with eurotophobia is kolpophobia; however; the scope of kolpophobia can sometimes be broader, allowing for the inclusion of all sex organs. Although eurotophobia does not have an interlingual classical compound, kolpophobia has a Greek etymological derivation with the prefix "kolpo" meaning a fold that usually alludes to the vulva. Eurotophobia is a hyponym of genitophobia. On the other hand, the term vaginaphobia is used to denote fear of female genitals in the context of sexual orientation. The male counterpart that analogously corresponds with this condition is called phallophobia.

AEN has never been recorded as a one symptom disorder, but instead present by multiple symptoms. The symptoms vary from the severity of the disorder. The most classic sign of AEN is the dark pigmentation of esophageal mucosa in an upper endoscopy, usually viewed as an ulcer or as an infectious disease. Necrosis can be found mostly between the three distals of the esophagus, but stops abruptly at the gastroesophageal junction. The basic and most common symptoms reported are blood in stool and blood in vomiting. Upper gastrointestinal bleeding then is reported, and is very commonly represented in elderly patients. Black or bloody stools and hematemesis account for over three quarters of the case presentations. Abdominal pain, nausea, vomiting, and unstable vital signs are common. A cardiovascular event (such as a heart attack) was reported in ten percent of the total known cases.

Thyroid disease in women is an autoimmune disease that affects the thyroid in women. This condition can have a profound effect during pregnancy and on the child. It also is called Hashimoto's thyroiditis (theye-royd-EYET-uhss). During pregnancy, the infant may be seriously affected and have a variety of birth defects. Many women with Hashimoto's disease develop an underactive thyroid. They may have mild or no symptoms at first, but symptoms tend to worsen over time. If a woman is pregnant and has symptoms of Hashimoto's disease, the clinician will do an exam and order one or more tests.

The thyroid is a small gland in the front of the neck. The thyroid makes hormones called T3 and T4 that regulate how the body uses energy. Thyroid hormone levels are controlled by the pituitary, which is a pea-sized gland in the brain. It makes thyroid stimulating hormone (TSH), which triggers the thyroid to make thyroid hormone.

In thyroid disease the immune system makes antibodies that damage thyroid cells and interfere with their ability to make thyroid hormone. Over time, thyroid damage can cause thyroid hormone levels to be too low. This is called an underactive thyroid or hypothyroidism (heye-poh-THEYE-royd-ism). An underactive thyroid causes every function of the body to slow down, such as heart rate, brain function, and the rate your body turns food into energy. Hashimoto's disease is the most common cause of an underactive thyroid. It is closely related to Graves' disease, another autoimmune disease affecting the thyroid.

Senile osteoporosis, formerly known as osteoporosis type II, has been recently recognized as a geriatric syndrome with a particular pathophysiology.

It has been pointed out that senile osteoporosis is the product of a skeleton in an advanced stage of life and also due to a deficiency caused by calcium, but physicians are also coming to the conclusion that multiple mechanisms in the development stages of the disease interact together and the product is an osteoporotic bone, regardless of age.

In the majority of young women, hyperandrogenism leads to oily skin, acne, hirutism, menstrual irregularities and, in some cases, androgenic alopecia, clitorimegaly, changes in muscle mass and deepening of the voice. Insulin resistance can be present in different forms; some persons have high concentrations of insulin but normal levels of glucose, while others have glucose measurements in the diabetic range. A history of diabetic symptoms such as polydipsia, polyuria and weight loss may sometimes, but not always, be present. Other related symptoms to HAIR-AN syndrome include enlarged clitoris, increased libido, glucose intolerance, irregular menstruation, increased blood pressure, infertility. Obesity is also one such symptoms in some women, and is also marked in women affected by PCOS, hirsutism, acanthosis nigricans.

Babies with this disorder are usually healthy at birth. The signs and symptoms may not appear until later in infancy or childhood and can include poor feeding and growth (failure to thrive), a weakened and enlarged heart (dilated cardiomyopathy), seizures, and low numbers of red blood cells (anemia). Another feature of this disorder may be very low blood levels of carnitine (a natural substance that helps convert certain foods into energy).

Isobutyryl-CoA dehydrogenase deficiency may be worsened by long periods without food (fasting) or infections that increase the body's demand for energy. Some individuals with gene mutations that can cause isobutyryl-CoA dehydrogenase deficiency may never experience any signs and symptoms of the disorder.

Phallophobia in its narrower sense is a fear of the erect penis and in a broader sense an excessive aversion to masculinity.

Acute esophageal necrosis can only be diagnosed by an upper gastrointestinal endoscopy.

Sigmund Freud has footnoted the possibility that this fear may be derived from a lack of ingenuity allowing one to ornamentally distance the copulatory organs from the excretory organs. Such a condition can affect both men and women. For others, symptoms include what characterizes a panic attack. It does not necessarily have to be induced by an uncovered penis, but may also result from seeing the manbulging outline or curvature of the penis, perhaps through clothes consisting of thin fabric. In more extreme cases it has been likened to the fight or flight response ingrained within the human body wherein an individual ceases to be intimate with their male partner and is unable to visit mixed gender establishments where people are likely to wear more revealing clothing, such as a gym, beach, cinema or livingrooms with a switched on monitor. The fear can recur through any of the senses including accidental touch, sight, hearing the word penis or thinking about an erection. The phobia may have developed from a condition such as dyspareunia, a trauma (usually sexual) that occurred during childhood, but can also have a fortuitous origin. In literature covering human sexuality, it is used as an adjective only to negatively allude to penetrative sex acts. Men who have the phobia may try to avoid wearing jeans and other light fabrics, especially in public. Some analysts have purported that the condition may be inherited or may be a combination of genetic inheritance and life experiences. For men with the condition, one of the byproducts is difficulty consummating with a partner due to a sense of vulnerability. This vulnerability may have developed during childhood because they grew up being told by their parents that sex and its physiological functions were evil, sinful and dirty, but were subsequently unable to detach such shameful feelings nor reverse it upon reaching adulthood, even when romantic initiatives were subsequently approved of or encouraged by their parents.

Carnitine-acylcarnitine translocase deficiency is a rare, autosomal recessive metabolic disorder that prevents the body from converting long-chain fatty acids into energy, particularly during periods without food. Carnitine, a natural substance acquired mostly through the diet, is used by cells to process fats and produce energy. People with this disorder have a faulty enzyme that prevents long-chain fatty acids from being transported into the innermost part of the mitochondria for processing.

A variety of neurological symptoms have been associated with carnosinemia. They include: hypotonia, developmental delay, mental retardation, degeneration of axons, sensory neuropathy, tremors, demyelinization, gray matter anomalies, myoclonic seizures, and loss of purkinje fibers.

Galactokinase deficiency, also known as Galactosemia type 2 or GALK deficiency, is an autosomal recessive metabolic disorder marked by an accumulation of galactose and galactitol secondary to the decreased conversion of galactose to galactose-1-phosphate by galactokinase. The disorder is caused by mutations in the GALK1 gene, located on chromosome 17q24. Galactokinase catalyzes the first step of galactose phosphorylation in the Leloir pathway of intermediate metabolism. Galactokinase deficiency is one of the three inborn errors of metabolism that lead to hypergalactosemia. The disorder is inherited as an autosomal recessive trait. Unlike classic galactosemia, which is caused by deficiency of galactose-1-phosphate uridyltransferase, galactokinase deficiency does not present with severe manifestations in early infancy. Its major clinical symptom is the development of cataracts during the first weeks or months of life, as a result of the accumulation, in the lens, of galactitol, a product of an alternative route of galactose utilization. The development of early cataracts in homozygous affected infants is fully preventable through early diagnosis and treatment with a galactose-restricted diet. Some studies have suggested that, depending on milk consumption later in life, heterozygous carriers of galactokinase deficiency may be prone to presenile cataracts at 20–50 years of age.

Low birth weight and a bird-like face may be the first signs. Severe intellectual deficit and death within the first decade are typical.

HAIR-AN syndrome consists of hyperandrogenism (HA), insulin resistance (IR), and acanthosis nigricans (AN). It is a rare disease which is a subset of poly-cystic ovary syndrome [PCOS]. Polycystic ovary syndrome is basically a condition in females which is arise by an increase in the production of androgen (male hormone), leading to an expression of male-like characters in the female body. The name HAIR-AN syndrome is made up of the three conditions of which it consists. The commonly used term "HAIR-AN" is a generic description of the features of SIR (severe insulin resistance)." In particular, although HAIR-AN results from two very different types of abnormalities - blocking antibodies against the insulin receptor OR genetically absent/reduced insulin receptor number/function - patients with "both" types have high levels of androgens (male hormones).

Research on the two types of HAIR-AN demonstrated that patients with both forms of HAIR-AN had very high levels of insulin and, critically, that it was the high insulin that caused the elevation in androgen. The patient affected by HAIR-AN syndrome has insulin resistance inside his or her body. Insulin resistance is a condition in which the body produces insulin but does not use it properly. This causes the pancreas to produce more insulin in the body. High levels of insulin stimulate the ovaries to make excess of androgen, leading to excessive hair growth, acne, and irregular periods in females body. Insulin resistance can also lead to diabetes, heart disease, and excessive growth and darkening of the skin (acanthosis nigricans)

Isobutyryl-coenzyme A dehydrogenase deficiency, commonly known as IBD deficiency, is a rare metabolic disorder in which the body is unable to process certain amino acids properly.

People with this disorder have inadequate levels of an enzyme that helps break down the amino acid valine, resulting in a buildup of valine in the urine, a symptom called valinuria.

Diabetic coma was a more significant diagnostic problem before the late 1970s, when glucose meters and rapid blood chemistry analyzers were not universally available in hospitals. In modern medical practice, it rarely takes more than a few questions, a quick look, and a glucose meter to determine the cause of unconsciousness in a patient with diabetes. Laboratory confirmation can usually be obtained in half an hour or less. Other conditions that can cause unconsciousness in a person with diabetes are stroke, uremic encephalopathy, alcohol, drug overdose, head injury, or seizure.

Fortunately, most episodes of diabetic hypoglycemia, DKA, and extreme hyperosmolarity do not reach unconsciousness before a family member or caretaker seeks medical help.

People with type 1 diabetes mellitus who must take insulin in full replacement doses are most vulnerable to episodes of hypoglycemia. It is usually mild enough to reverse by eating or drinking carbohydrates, but blood glucose occasionally can fall fast enough and low enough to produce unconsciousness before hypoglycemia can be recognized and reversed. Hypoglycemia can be severe enough to cause unconsciousness during sleep. Predisposing factors can include eating less than usual or prolonged exercise earlier in the day. Some people with diabetes can lose their ability to recognize the symptoms of early hypoglycemia.

Unconsciousness due to hypoglycemia can occur within 20 minutes to an hour after early symptoms and is not usually preceded by other illness or symptoms. Twitching or convulsions may occur. A person unconscious from hypoglycemia is usually pale, has a rapid heart beat, and is soaked in sweat: all signs of the adrenaline response to hypoglycemia. The individual is not usually dehydrated and breathing is normal or shallow. Their blood sugar level, measured by a glucose meter or laboratory measurement at the time of discovery, is usually low but not always severely, and in some cases may have already risen from the nadir that triggered the unconsciousness.

Unconsciousness due to hypoglycemia is treated by raising the blood glucose with intravenous glucose or injected glucagon.

Individuals with Salla disease may present with nystagmus in the first months of life as well as hypotonia, reduced muscle tone and strength, and cognitive impairment. The most severely impaired children do not walk or acquire language, but the typical patient learns to walk and speak and has normal life expectancy. The MRI shows arrested or delayed myelination.

The syndrome is characterized by alopecia, hypogonadism, hypothyroidism, hearing loss, intellectual disability and diabetes mellitus. Electrocardiogram anomalies have also been reported.

Galactokinase deficiency is an autosomal recessive disorder, which means the defective gene responsible for the disorder is located on an autosome (chromosome 17 is an autosome), and two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder.

Unlike galactose-1-phosphate uridyltransferase deficiency, the symptoms of galactokinase deficiency are relatively mild. The only known symptom in affected children is the formation of cataracts, due to production of galactitol in the lens of the eye. Cataracts can present as a failure to develop a social smile and failure to visually track moving objects.