The lateral femoral cutaneous nerve most often becomes injured by entrapment or compression where it passes between the upper front hip bone (ilium) and the inguinal ligament near the attachment at the anterior superior iliac spine (the upper point of the hip bone). Less commonly, the nerve may be entrapped by other anatomical or abnormal structures, or damaged by diabetic or other neuropathy or trauma such as from seat belt injury in an accident.

The nerve may become painful over a period of time as weight gain makes underwear, belting or the waistband of pants gradually exert higher levels of pressure. Pain may be acute and radiate into the rib cage, and into the groin, thigh, and knee. Alternately, weight loss or aging may remove protective fat layers under the skin, so the nerve can compress against underwear, outer clothing, and—most commonly— by belting. Long periods of standing or leg exercise that increases tension on the inguinal ligament may also cause pressure.

Other causes may include:

- Anticonvulsant pharmaceutical drugs, such as topiramate, sultiame, and acetazolamide

- Anxiety and/or panic disorder

- Benzodiazepine withdrawal syndrome

- Beta alanine

- Carpal tunnel syndrome

- Cerebral amyloid angiopathy

- Chiari malformation

- Coeliac disease (celiac disease)

- Complex regional pain syndrome

- Decompression sickness

- Dehydration

- Dextromethorphan (recreational use)

- Fabry disease

- Erythromelalgia

- Fibromyalgia

- Fluoroquinolone toxicity

- Guillain–Barré syndrome (GBS)

- Heavy metals

- Herpes zoster

- Hydroxy alpha sanshool, a component of Sichuan peppers

- Hyperglycemia (high blood sugar)

- Hyperkalemia

- Hyperventilation

- Hypoglycemia (low blood sugar)

- Hypocalcemia, and in turn:

- Hypermagnesemia, a condition in which hypocalcemia itself is typically observed as a secondary symptom

- Hypomagnesemia, often as a result of long term proton-pump inhibitor use

- Hypothyroidism

- Immunodeficiency, such as chronic inflammatory demyelinating polyneuropathy (CIDP)

- Intravenous administering of strong pharmaceutical drugs acting on the central nervous system (CNS), mainly opioids, opiates, narcotics; especially in non-medical use (drug abuse)

- Ketorolac

- Lidocaine poisoning

- Lomotil

- Lupus erythematosus

- Lyme disease

- Menopause

- Mercury poisoning

- Migraines

- Multiple sclerosis

- Nitrous oxide, long-term exposure

- Obdormition

- Pyrethrum and pyrethroid (pesticide)

- Rabies

- Radiation poisoning

- Sarcoidosis

- Scorpion stings

- Spinal disc herniation or injury

- Spinal stenosis

- Stinging nettles

- Syringomyelia

- Transverse myelitis

- Vitamin B deficiency

- Vitamin B deficiency

- Withdrawal from certain selective serotonin reuptake inhibitors (or serotonin-specific reuptake inhibitors) (SSRIs), such as paroxetine or serotonin-norepinephrine reuptake inhibitors (SNRIs) such as venlafaxine

The entire distribution of the nerve is rarely affected. Usually, the unpleasant sensation(s) affect only part of the skin supplied by the nerve.

Paresthesia or "persistent anesthesia" is a transient or potentially permanent condition of extended numbness after administration of local anesthesia and the injected anesthetic has terminated.

Potential causes include trauma induced to the nerve sheath during administration of the injection, hemorrhage about the sheath, type of anesthetic used, or administration of anesthetic potentially contaminated with alcohol or sterilizing solutions.

Harlequin syndrome is a condition characterized by asymmetric sweating and flushing on the upper thoracic region of the chest, neck, and face. Harlequin syndrome is considered an injury to the autonomic nervous system (ANS). The ANS controls some of the body's natural processes such as sweating, skin flushing, and pupil response to stimuli. Such individuals with this syndrome have an absence of sweat skin flushing unilaterally; usually on the one side of the face, arms, and chest. It is an autonomic disorder that may occur at any age. Harlequin syndrome affects fewer than 200,000 people in the United States.

Symptoms associated with Harlequin syndrome are more likely to appear when a person has been in the following conditions: exercising, warm environment, and intense emotional situation. Since one side of the body sweats and flushes appropriately to the condition, the other side of the body will have an absence of such symptoms. This syndrome has also been called the "Harlequin sign," and thought to be one of the spectrum of diseases that may cause Harlequin syndrome.

It can also be the outcome of a one sided endoscopic thoracic sympathectomy (ETS) or endoscopic sympathetic blockade (ESB) surgery.

Harlequin syndrome can also be seen as a complication of VA (veno-arterial) extracorporeal membrane oxygenation (ECMO). This involves differential hypoxemia (low oxygen levels in the blood) of the upper body in comparison to the lower body.

Although the exact mechanism for Harlequin syndrome is still unclear, understanding what is affected with this syndrome is important. Majority of cases are thought to occur when nerve bundles in the head and neck are injured. Such bundles are able to send an action potential from the autonomic nervous system to the rest of the body. However, action potentials in this system are not being received by the second or third thoracic vertebrae which innervates the face, neck, and upper chest. Damage or lesions near T2 or T3 could be between the stellate ganglion and superior cervical ganglion. This is where we would observe absence of sweat and skin flushing on one side of the face, neck, and upper chest. Harlequin Syndrome may be classified as the following: Primary, Idiopathic, Congenital, Secondary, Organic lesion, Iatrogenic cause.

The specific cause of camptodactyly remains unknown, but there are a few deficiencies that lead to the condition. A deficient lumbrical muscle controlling the flexion of the fingers, and abnormalities of the flexor and extensor tendons.

A number of congenital syndromes may also cause camptodactyly:

- Jacobsen syndrome

- Beals Syndrome

- Blau syndrome

- Freeman-Sheldon syndrome

- Cerebrohepatorenal syndrome

- Weaver syndrome

- Christian syndrome 1

- Gordon Syndrome

- Jacobs arthropathy-camptodactyly syndrome

- Lenz microphthalmia syndrome

- Marshall-Smith-Weaver syndrome

- Oculo-dento-digital syndrome

- Tel Hashomer camptodactyly syndrome

- Toriello-Carey syndrome

- Stuve-Wiedemann syndrome

- Loeys-Dietz syndrome

- Fryns syndrome

- Marfan's syndrome

- Carnio-carpo-tarsal dysthropy

Camptodactyly is a medical condition that causes one or more fingers to be permanently bent. It involves fixed flexion deformity of the proximal interphalangeal joints. The fifth finger is always affected.

Camptodactyly can be caused by a genetic disorder. In that case, it is an autosomal dominant trait that is known for its incomplete genetic expressivity. This means that when a person has the genes for it, the condition may appear in both hands, one, or neither. A linkage scan proposed that the chromosomal locus of camptodactyly was 3q11.2-q13.12.

In the United States, sarcoidosis has a prevalence of approximately 10 cases per 100,000 whites and 36 cases per 100,000 blacks. Heerfordt syndrome is present in 4.1–5.6% of those with sarcoidosis.

There is considerable research into the causes, diagnosis and treatments for FGIDs. Diet, microbiome, genetics, neuromuscular function and immunological response all interact. Heightened mast cell activation has been proposed to be a common factor among FGIDs, contributing to visceral hypersensitivity as well as epithelial, neuromuscular, and motility dysfunction.

The exact cause of Heerfordt syndrome has not yet been definitively determined. Of those patients who have been diagnosed with Heerfordt syndrome, 15% have a close relative who also has the syndrome. One possible explanation is that the syndrome results from a combination of an environmental agent and a hereditary predisposition. "Mycobacterium" and "Propionibacteria" species have both been suggested as the environmental agent, though the evidence for this is inconclusive.

Respiratory complications are often cause of death in early infancy.

Functional gastrointestinal disorders are very common. Globally, irritable bowel syndrome and functional dyspepsia alone may affect 16–26% of the population.

The first gene that could cause the syndrome is described recently and is called NF1X (chromosome 19: 19p13.1).

Males are twice as likely as females to have this characteristic, and it tends to run in families. In its non-symptomatic form, it is more common among Asians and Native Americans than among other populations, and in some families there is a tendency to inherit the condition unilaterally, that is, on one hand only.

The presence of a single transverse palmar crease can be, but is not always, a symptom associated with abnormal medical conditions, such as fetal alcohol syndrome, or with genetic chromosomal abnormalities, including Down Syndrome (chromosome 21), cri du chat syndrome (chromosome 5), Klinefelter syndrome, Wolf-Hirschhorn Syndrome, Noonan syndrome (chromosome 12), Patau syndrome (chromosome 13), IDIC 15/Dup15q (chromosome 15), Edward's syndrome (chromosome 18), and Aarskog-Scott syndrome (X-linked recessive), or autosomal recessive disorder, such as Leaukocyte adhesion deficiency-2 (LAD2). A unilateral single palmar crease was also reported in a case of chromosome 9 mutation causing Nevoid basal cell carcinoma syndrome and Robinow syndrome. It is also sometimes found on the hand of the affected side of patients with Poland Syndrome, and craniosynostosis.

In humans, a single transverse palmar crease is a single crease that extends across the palm of the hand, formed by the fusion of the two palmar creases (known in palmistry as the "heart line" and the "head line") and is found in people with Down Syndrome. It is also found in 1.5% of the general population in at least one hand.

Because it resembles the usual condition of non-human simians, it is also known as a simian crease or simian line, although these terms have widely fallen out of favor due to their pejorative connotation.

Marshall syndrome is a genetic disorder of the connective tissue which can cause hearing loss. The three most common areas to be affected are the eyes which are uncommonly large, joints and the mouth and facial structures. Marshall syndrome and Stickler syndrome closely resemble each other; in fact they are so similar, some say they are the same.

Muir–Torre was observed to occur in 14 of 50 families (28%) and in 14 of 152 individuals (9.2%) with Lynch syndrome, also known as HNPCC.

The 2 major MMR proteins involved are hMLH1 and hMSH2. Approximately 70% of tumors associated with the MTS have microsatellite instability. While germline disruption of hMLH1 and hMSH2 is evenly distributed in HNPCC, disruption of hMSH2 is seen in greater than 90% of MTS patients.

Gastrointestinal and genitourinary cancers are the most common internal malignancies. Colorectal cancer is the most common visceral neoplasm in Muir–Torre syndrome patients.

Café au lait spots can arise from diverse and unrelated causes:

- Having six or more café au lait spots greater than 5 mm in diameter before puberty, or greater than 15 mm in diameter after puberty, is a diagnostic feature of neurofibromatosis type I, but other features are required to diagnose NF-1.

- Familial multiple café au lait spots have been observed without NF-1 diagnosis.

- They can be caused by vitiligo in the rare McCune–Albright syndrome.

- Legius syndrome

- Tuberous sclerosis

- Fanconi anemia

- Idiopathic

- Ataxia-telangiectasia

- Basal cell nevus syndrome

- Benign congenital skin lesion

- Bloom syndrome

- Chédiak–Higashi syndrome

- Congenital naevus

- Gaucher disease

- Hunter syndrome

- Jaffe–Campanacci syndrome

- Maffucci syndrome

- Multiple mucosal neuroma syndrome

- Noonan syndrome

- Pulmonary Stenosis

- Silver–Russell syndrome

- Watson syndrome

- Wiskott–Aldrich syndrome

Shawl scrotum is a condition in which the scrotum surrounds the penis, resembling a 'shawl'.

It is a characteristic of some syndromes such as Aarskog-Scott syndrome (faciodigitogenital syndrome), Rubenstein-Taybi syndrome, craniofrontonasal dysplasia, Hunter Carpenter McDonald Syndrome, Naguib Syndrome, Saito Kuba Tsuruta Syndrome, Ieshima Koeda Inagaki syndrome, Cystic fibrosis Gastritis Megaloblastic Anemia, Willems de Vries syndrome, Schinzel syndrome and Seaver Cassidy syndrome.

Anticholinergic drugs have been reported to be extremely effective in 40% of the patients with the Pisa syndrome. Patients with Pisa syndrome that is resistant to anticholinergic drugs is mostly resolved by the reduction of the administration of the antipsychotic drugs as previously mentioned. While the specific pathology underlying idiopathic Pisa syndrome is unknown, the administration of anticholinergic drugs has provided resolution in known cases.

Café au lait spots are usually present at birth, permanent, and may grow in size or increase in number over time.

Cafe au lait spots are themselves benign and do not cause any illness or problems. However, they may be associated with syndromes such as Neurofibromatosis Type 1 and McCune-Albright syndrome.

The size and shape of the spots do not have any meaning or implications with regards to diagnosis of associated syndromes.

Many conditions affect the human integumentary system—the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment. The skin weighs an average of four kilograms, covers an area of two square meters, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. The two main types of human skin are: glabrous skin, the hairless skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin. Within the latter type, the hairs occur in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle. In the embryo, the epidermis, hair, and glands form from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues.

The epidermis is the most superficial layer of skin, a squamous epithelium with several strata: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. Nourishment is provided to these layers by diffusion from the dermis, since the epidermis is without direct blood supply. The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Of these, keratinocytes are the major component, constituting roughly 95 percent of the epidermis. This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface. In normal skin, the rate of production equals the rate of loss; about two weeks are needed for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional two weeks to cross the stratum corneum.

The dermis is the layer of skin between the epidermis and subcutaneous tissue, and comprises two sections, the papillary dermis and the reticular dermis. The superficial papillary dermis with the overlying rete ridges of the epidermis, between which the two layers interact through the basement membrane zone. Structural components of the dermis are collagen, elastic fibers, and ground substance. Within these components are the pilosebaceous units, arrector pili muscles, and the eccrine and apocrine glands. The dermis contains two vascular networks that run parallel to the skin surface—one superficial and one deep plexus—which are connected by vertical communicating vessels. The function of blood vessels within the dermis is fourfold: to supply nutrition, to regulate temperature, to modulate inflammation, and to participate in wound healing.

The subcutaneous tissue is a layer of fat between the dermis and underlying fascia. This tissue may be further divided into two components, the actual fatty layer, or panniculus adiposus, and a deeper vestigial layer of muscle, the panniculus carnosus. The main cellular component of this tissue is the adipocyte, or fat cell. The structure of this tissue is composed of septal (i.e. linear strands) and lobular compartments, which differ in microscopic appearance. Functionally, the subcutaneous fat insulates the body, absorbs trauma, and serves as a reserve energy source.

Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails). While only a small number of skin diseases account for most visits to the physician, thousands of skin conditions have been described. Classification of these conditions often presents many nosological challenges, since underlying etiologies and pathogenetics are often not known. Therefore, most current textbooks present a classification based on location (for example, conditions of the mucous membrane), morphology (chronic blistering conditions), etiology (skin conditions resulting from physical factors), and so on. Clinically, the diagnosis of any particular skin condition is made by gathering pertinent information regarding the presenting skin lesion(s), including the location (such as arms, head, legs), symptoms (pruritus, pain), duration (acute or chronic), arrangement (solitary, generalized, annular, linear), morphology (macules, papules, vesicles), and color (red, blue, brown, black, white, yellow). Diagnosis of many conditions often also requires a skin biopsy which yields histologic information that can be correlated with the clinical presentation and any laboratory data.

The Kocher–Debré–Semelaigne syndrome is hypothyroidism in infancy or childhood characterised by lower extremity or generalized muscular hypertrophy, myxoedema, short stature and cretinism. The absence of painful spasms and pseudomyotonia differentiates this syndrome from its adult form, which is Hoffmann syndrome.

The syndrome is named after Emil Theodor Kocher, Robert Debré and Georges Semelaigne.

Also known as Debre–Semelaigne syndrome or cretinism-muscular hypertrophy, hypothyroid myopathy, hypothyroidism-large muscle syndrome, hypothyreotic muscular hypertrophy in children, infantile myxoedema-muscular hypertrophy, myopathy-myxoedema syndrome, myxoedema-muscular hypertrophy syndrome, myxoedema-myotonic dystrophy syndrome.

Kocher-Debre-Semelaigne syndrome gives infant a Hercules appearance.

Schimmelpenning syndrome appears to be sporadic rather than inherited, in almost all cases. It is thought to result from genetic mosaicism, possibly an autosomal dominant mutation arising after conception and present only in a subpopulation of cells. The earlier in embryological development such a mutation occurs, the more extensive the nevi are likely to be and the greater the likelihood of other organ system involvement.