Clinical lycanthropy is defined as a rare psychiatric syndrome that involves a delusion that the affected person can transform into, has transformed into, or is a non-human animal. Its name is associated with the mythical condition of lycanthropy, a supernatural affliction in which humans are said to physically shapeshift into wolves. It is purported to be a rare disorder.

One important factor may be differences or changes in parts of the brain known to be involved in representing body shape (e.g., see proprioception and body image). A neuroimaging study of two people diagnosed with clinical lycanthropy showed that these areas display unusual activation, suggesting that when people report their bodies are changing shape, they may be genuinely perceiving those feelings.

Species dysphoria is the experience of dysphoria, sometimes including clinical lycanthropy (delusion or hallucination of one's self as an animal) and dysmorphia (excessive concern over one's body image), associated with the feeling that one's body is of the wrong species. Earls and Lalumière (2009) describe it as "the sense of being in the wrong (species) body... a desire to be an animal". Outside of psychological literature, the term is common within the otherkin and therian communities. The phenomenon is sometimes experienced in the context of sexual arousal to the image of one's self as an animal.

Clinical vampirism, more commonly called Renfield's syndrome or Renfield syndrome, is an obsession with drinking blood. The earliest formal presentation of clinical vampirism to appear in the psychiatric literature, with the psychoanalytic interpretation of two cases, was contributed by Richard L. Vanden Bergh and John F. Kelley in 1964. As the authors point out, brief and sporadic reports of blood-drinking behaviors associated with sexual pleasure have appeared in the psychiatric literature at least since 1892 with the work of Austrian forensic psychiatrist Richard von Krafft-Ebing. Many medical publications concerning clinical vampirism can be found in the literature of forensic psychiatry, with the unusual behavior reported as one of many aspects of extraordinary violent crimes. The behavior has never gained official recognition by the psychiatric profession and is not found in any edition of the "International Classification of Diseases" or the "Diagnostic and Statistical Manual of Mental Disorders".

"Species dysphoria" is informally used mainly in psychological literature to compare the experiences of some individuals to those in the transgender community. Otherkin and therian communities have also used it to describe their experiences.

In a 2008 study by Gerbasi "et al.", 46% of people surveyed who identified as being in the furry fandom, (usually defined as a person who enjoys anthropomorphic animals, occasionally to an almost obsessive degree), answered "yes" to the question "Do you consider yourself to be less than 100% human?" and 41% answered "yes" to the question "If you could become 0% human, would you?" Questions that Gerbasi states as being deliberately designed to draw parallels with gender dysphoria, specifying "a persistent feeling of discomfort" about the human body and the feeling that the person was the "non-human species trapped in a human body", were answered "yes" by 24% and 29% of respondents, respectively. Likewise, these studies support the fact that the therianthropic, otherkin and furry communities are very similar in nature and are often interconnected.

As described by those who experience it, species dysphoria may include sensations of supernumerary phantom limbs associated with the species, such as phantom wings or claws. Species dysphoria involves feelings of being an animal or other creatures "trapped in" a human body and so, is considered different from the traditional definition of clinical lycanthropy, in which the patient believes they have actually been transformed into an animal or have the ability to physically shapeshift. However, some cases that have been labeled as "clinical lycanthropy" actually seem to be cases of species dysphoria, involving persons who have no delusion of transformation but instead have feelings of being in some way a non-human animal, while still acknowledging they possess a human form. Keck "et al." propose a redefinition for clinical lycanthropy that covers species dysphoric behaviours observed in several patients, including verbal reports, "during intervals of lucidity or retrospectively, that he or she was a particular animal" and behaving "in the manner of a particular animal, i.e. howling, growling, crawling on all fours". Keck "et al." describe one patient as a depressed individual who "had always suspected he was a cat" and "laments his lack of fur, stripes and a tail". Except for the persistent feeling of being feline, the patient's "thought processes and perception" were "usually logical".

Involutional melancholy's 'course was chronic, with agitation, depersonalization and delusions of bodily change and guilt' featuring strongly, but 'without manic features'. Symptoms of fear are also considered to occur, as well as despondency and hypochondriacal delusions. The late onset of the disorder was matched with a prolonged course with poor prognosis and/or deterioration, in the absence of treatment.

Involutional melancholia is classically treated with antidepressants and mood elevators.

Electroconvulsive therapy may also be used. Mid-century, there was a consensus that the technique indeed 'yields the best results in the long-lasting depressions of the change of life, the so-called "involutional melancholias", which before this form of treatment was introduced often required years of hospitalization'. The 21st century also records 'an excellent and rapid clinical response found in melancholia of recent onset...in older rather than younger patients' with ECT

Cynanthropy (sometimes spelled "kynanthropy") is, in medicine, the pathological delusion of real persons that they are dogs and in anthropology and folklore, the supposed magical practice of shape-shifting alternately between canine and human form, or the possession of combined canine and human anatomical features, a form of therianthropy.

The Greeks spoke of cynanthropy ("kyon", dog). The term existed by at least 1901, when it was applied to myths from China about humans turning into dogs, dogs becoming people, and sexual relations between humans and canines (De Groot, 184). After lycanthropy, cynanthropy is the best known term for a specific variety of therianthropy.

Anthropologist David Gordon White called Central Asia the "vortex of cynanthropy" because races of dog-men were habitually placed there by ancient writers. Hindu mythology puts races of "Dog Cookers" to the far north of India, the Chinese placed the "Dog Jung" and other human/canine barbarians to the extreme west, and European legends frequently put the dog men called Cynocephali in unmapped regions to the east. Some of these races were described as humans with dog heads, others as canine shapeshifters (White, 114-15).

The weredog or cynanthrope is also known in Timor. It is described as a human/canine shapeshifter who is also capable of transforming other people into animals against their wills. These transformations are usually into prey animals such as goats, so that the cynanthrope can devour them without discovery of the crime (Rose, 390).

Somatic manifestations of MD are distinguished by an extreme diversity and include headaches, back pain, abdominal pain etc. Pathological behaviour masking depression may take the form of compulsive gambling, compulsive work, changes in arousal or orgasmic function, decreased libido or, on the contrary, impulsive sexual behaviour, alcoholism, drug addiction and more.

Masked depression (MD) was a proposed form of atypical depression in which somatic symptoms or behavioural disturbances dominate the clinical picture and disguise the underlying affective disorder. The concept is not currently supported by the mental health profession.

Very few cases of the syndrome have been described, and the published reports that do exist describe clinical vampirism as behaviors that are subsumed under more conventional psychiatric diagnostic categories such as schizophrenia or paraphilia. A case of vampirism in Turkey reported in 2012 was discussed as an unusual feature of a patient diagnosed with dissociative identity disorder and post-traumatic stress disorder. While not referencing the literature on Renfield's syndrome, two Irish psychiatrists surveyed the psychiatric literature on vampirism as evidence of a changing discourse in psychiatry from the narrative of case studies to the depersonalized discourse of checklist diagnostic criteria.

A number of murderers have performed seemingly vampiric rituals upon their victims. Serial killers Peter Kürten and Richard Trenton Chase were both called "vampires" in the tabloids after they were discovered drinking the blood of the people they murdered. Similarly, in 1932, an unsolved murder case in Stockholm, Sweden was nicknamed the "Vampire murder", due to the circumstances of the victim's death.Clinical vampirism in the context of criminal acts of violence, as well as "consensual" vampirism as a social ritual, have been extensively documented in the many works of Katharine Ramsland. Others have commented upon the psychiatric implications of "vampire cults" among adolescents.

MCI does not usually interfere with daily life, but around 50 percent of people diagnosed with it go on to develop the far more severe Alzheimer's disease within five years. However, some instances of MCI may simply remain stable over time or even remit.

The prevalence of MCI varies by age. The prevalence of MCI among different age groups is as follows: 6.7% for ages 60–64; 8.4% for ages 65–69, 10.1% for ages 70–74, 14.8% for ages 75–79, and 25.2% for ages 80–84. After a two-year follow-up, the cumulative incidence of dementia among individuals who are over 65 years old and were diagnosed with MCI was found to be 14.9%.

Globally, approximately 16% of the population over the age of 70 experiences some type of mild cognitive impairment.

What is considered objective insomnia, unlike SSM, can easily be confirmed empirically through clinical testing, such as by polysomnogram. Those who experience SSM may believe that they have not slept for extended periods of time, when they in fact do sleep but without perceiving it. For example, while patients who claim little or no sleep may usually acknowledge impaired job performance and daytime drowsiness, sleep state misperceivers often do not.

Cases of objective total insomnia are extremely rare. The few that have been recorded have predominantly been ascribed to a rare incurable genetic disorder called fatal familial insomnia, which patients rarely survive for more than 26 months after the onset of illness—often much less. While rarer cases of objective total insomnia lasting for decades have been reported, such as with the American Al Herpin and the Vietnamese Thai Ngoc, they have not been studied extensively in a clinical setting.

SSM is poorly understood. As of 2008, there is little to no information regarding risk factors or prevention, though it is believed to be most prevalent among young to middle aged adults.

Distribution among the general population and by gender is unknown. About 5% of the clinical population may be affected, though that figure is subject to sampling bias.

Heterogeneous medical condition in medicine are those medical conditions which have several etiologies, like hepatitis or diabetes. Medical conditions are normally defined pathologically (liver inflammation) or clinically (excessive urination) and not etiologically, and therefore it is normal to have more than one cause for them. The word is used as an opposition to homogeneous, meaning that given a group of patients, the disease is the same for all of them.

When a condition is heterogeneous, it is normally divided in endotypes.

The progression of symptoms varies widely between each case of FXTAS; the onset of symptoms may be gradual, with progression of the disease spanning multiple years or decades. Alternatively, symptoms may progress rapidly.

FXTAS has shown strong age-dependent penetrance, afflicting older permutation carriers with greater prevalence. Male carriers, age 50 and above have a 30% chance of acquiring FXTAS, while male carriers, age 75 and above, have a 75% chance of developing FXTAS. While initially described to affect male carriers, female carriers of the FMR1 gene mutation have also been found to develop FXTAS. However, due to X-inactivation, female carriers are much less likely to develop classic ataxia and tremor signs for FXTAS, instead demonstrating symptoms such as fibromyalgia, thyroid disease, hypertension, and seizures.

In examining the published studies on opioid-induced hyperalgesia (OIH), Reznikov "et al" criticize the methodologies employed on both humans and animals as being far-removed from the typical regimen and dosages of pain patients in the real world. They also note that some OIH studies were performed on drug addicts in methadone rehabilitation programs, and that such results are very difficult to generalize and apply to medical patients in chronic pain. In contrast, a study of 224 chronic pain patients receiving 'commonly-used' doses of oral opioids, in more typical clinical scenarios, found that the opioid-treated patients actually experienced no difference in pain sensitivity when compared to patients on non-opioid treatments. The authors conclude that opioid-induced hyperalgesia may not be an issue of any significance for normal, medically-treated chronic pain patients at all.

Opioid-induced hyperalgesia has also been criticized as overdiagnosed among chronic pain patients, due to poor differential practice in distinguishing it from the much more common phenomenon of opioid tolerance. The misdiagnosis of common opioid tolerance (OT) as opioid-induced hyperalgesia (OIH) can be problematic as the clinical actions suggested by each condition can be contrary to each other. Patients misdiagnosed with OIH may have their opioid dose mistakenly decreased (in the attempt to counter OIH) at times when it is actually appropriate for their dose to be increased or rotated (as a counter to opioid tolerance).

The suggestion that chronic pain patients who are diagnosed as experiencing opioid-induced hyperalgesia ought to be completely withdrawn from opioid therapy has also been met with criticism. This is not only because of the uncertainties surrounding the diagnosis of OIH in the first place, but because of the viability of rotating the patient between different opioid analgesics over time. Opioid rotation is considered a valid alternative to the reduction or cessation of opioid therapy, and multiple studies demonstrate the rotation of opioids to be a safe and effective protocol.

An endotype is a subtype of a condition, which is defined by a distinct functional or pathobiological mechanism. This is distinct from a phenotype, which is any observable characteristic or trait of a disease, such as morphology, development, biochemical or physiological properties, or behavior, without any implication of a mechanism. It is envisaged that patients with a specific endotype present themselves within phenotypic clusters of diseases.

One example is asthma, which is considered to be a syndrome, consisting of a series of endotypes. This is related to the concept of disease entity

As of June 2014 (the latest update on HFM in GeneReviews) a total of 32 families had been reported with a clinical diagnosis of HFM of which there was genotypic confirmation in 24 families. Since then, another two confirmed cases have been reported and an additional case was reported based on a clinical diagnosis alone. Most cases emerge from consanguineous parents with homozygous mutations. There are three instances of HFM from non-consanguineous parents in which there were heterozygous mutations. HFM cases are worldwide with mostly private mutations. However, a number of families of Puerto Rican ancestry have been reported with a common pathogenic variant at a splice receptor site resulting in the deletion of exon 3 and the absence of transport function. A subsequent population-based study of newborn infants in Puerto Rico identified the presence of the same variant on the island. Most of the pathogenic variants result in a complete loss of the PCFT protein or point mutations that result in the complete loss of function. However, residual function can be detected with some of the point mutants.

The true prevalence of PMS has not been determined. More than 1200 people have been identified worldwide according the Phelan-McDermid Syndrome Foundation. However, it is believed to be underdiagnosed due to inadequate genetic testing and lack of specific clinical features. It is known to occur with equal frequency in males and females. Studies using chromosomal microarray for diagnosis indicate that at least 0.5% of cases of ASD can be explained by mutations or deletions in the "SHANK3" gene. In addition when ASD is associated with ID, "SHANK3" mutations or deletions have been found in up to 2% of individuals.

Singleton Merten Syndrome is an autosomal dominate genetic disorder with variable expression with an onset of symptoms during childhood.

Opioid-induced hyperalgesia or opioid-induced abnormal pain sensitivity, also called paradoxical hyperalgesia is a phenomenon associated with the long-term use of opioids such as morphine, hydrocodone, oxycodone, and methadone. Over time, individuals taking opioids can develop an increasing sensitivity to noxious stimuli, even evolving a painful response to previously non-noxious stimuli (allodynia). Some studies on animals have also demonstrated this effect occurring after only a single high dose of opioids.

Tolerance, another condition that can arise from prolonged exposure to opioids, can often be mistaken for opioid-induced hyperalgesia and vice-versa, as the clinical presentation can appear similar. Although tolerance and opioid-induced hyperalgesia both result in a similar need for dose escalation to receive the same level of effect to treat pain, they are nevertheless caused by two distinct mechanisms. The similar net effect makes the two phenomena difficult to distinguish in a clinical setting. Under chronic opioid treatment, a particular individual's requirement for dose escalation may be due to tolerance, opioid-induced hyperalgesia, or a combination of both. In tolerance, there is a lower sensitivity to opioids, which occurs via two major theories: decreased receptor activation (desensitization of antinociceptive mechanisms), and opioid receptor down-regulation (internalization of membrane receptors). In opioid-induced hyperalgesia, sensitization of pronociceptive mechanisms occurs, resulting in a decrease in the pain threshold, or allodyna. Identifying the development of hyperalgesia is of great clinical importance since patients receiving opioids to relieve pain may paradoxically experience more pain as a result of treatment. Whereas increasing the dose of opioid can be an effective way to overcome tolerance, doing so to compensate for opioid-induced hyperalgesia may worsen the patient's condition by increasing sensitivity to pain while escalating physical dependence.

The phenomenon is common among palliative care patients following a too rapid escalation of opioid dosage.

HPS is one of the rare lung diseases currently being studied by The Rare Lung Diseases Consortium (RLDC). The RLDC is part of the Rare Diseases Clinical Research Network (RDCRN), an initiative of the Office of Rare Diseases Research (ORDR), of the National Center for Advancing Translational Sciences (NCATS). The RLDC is dedicated to developing new diagnostics and therapeutics for patients with rare lung diseases, through collaboration between the NIH, patient organizations and clinical investigators.

The course of HPS has been mild in rare instances of the disorder, however, the general prognosis is still considered to be poor.

The disease can cause dysfunctions of the lungs, intestine, kidneys, and heart. The major complication of most forms of the disorder is pulmonary fibrosis, which typically exhibits in patients ages 40–50 years. This is a fatal complication seen in many forms of HPS, and is the usual cause of death from the disorder. HPS patients who develop pulmonary fibrosis typically have type 1 or type 4.