Individual susceptibility to HAPE is difficult to predict. The most reliable risk factor is previous susceptibility to HAPE, and there is likely to be a genetic basis to this condition, perhaps involving the gene for angiotensin converting enzyme (ACE). Recently, scientists have found the similarities between low amounts of 2,3-BPG (also known as 2,3-DPG) with the occurrence of HAPE at high altitudes. Persons with sleep apnea are susceptible due to irregular breathing patterns while sleeping at high altitudes.

The incidence of clinical HAPE in unacclimatized travelers exposed to high altitude (~) appears to be less than 1%. The U.S. Army Pike's Peak Research Laboratory has exposed sea-level-resident volunteers rapidly and directly to high altitude; during 30 years of research involving about 300 volunteers (and over 100 staff members), only three have been evacuated with suspected HAPE.

Oedema Glottidis is defined as the abnormal accumulation of fluid in tissues involving the supraglottic and subglottic region where laryngeal mucosa is loose. It is also known as Laryngeal Oedema.

Pulmonary aspiration of acidic material (such as stomach acid) may produce an immediate primary injury caused by the chemical reaction of acid with lung parenchyma, and a later secondary injury as a result of the subsequent inflammatory response.

Risk factors for pulmonary aspiration include conditions which depress the level of consciousness (such as traumatic brain injury, alcohol intoxication, drug overdose, and general anesthesia). A decreased gag reflex, upper esophageal sphincter and lower esophageal sphincter tone, gastroesophageal reflux, full stomach, as well as obesity, stroke, and pregnancy can all increase the risk of aspiration in the semiconscious. Tracheal intubation or presence of a gastric tube (for example, a feeding tube) may also increase the risk.

Both sex are equally affected

Any age group can develop a parapheryngeal abscess but it is most commonly seen in children and adolescents. Adults who are immunocompromised are also at high risk.

The pathogenesis of this disease is unclear. Arteriosclerosis obliterans has been postulated as the cause, along with errors of the clotting and fibrinolytic pathways such as antiphospholipid syndrome.

Infection can occur from:

- Pharynx: acute and chronic infection of tonsil and adenoids

- Teeth: dental infection occurs from lower last molar tooth

- Ear: bezold abscess and petrositis

- Other space: infection of parotid retropharyngeal space

- External trauma: penetrating injuries of neck, injection of local anaesthetic

Purpura hemorrhagica may be prevented by proper management during an outbreak of strangles. This includes isolation of infected horses, disinfection of fomites, and good hygiene by caretakers. Affected horses should be isolated at least one month following infection. Exposed horses should have their temperature taken daily and should be quarantined if it becomes elevated. Prophylactic antimicrobial treatment is not recommended.

Vaccination can reduce the incidence and severity of the disease. However, horses with high SeM antibody titers are more likely to develop purpura hemorrhagica following vaccination and so these horses should not be vaccinated. Titers may be measured by ELISA.

Prognosis is good with early, aggressive treatment (92% survival in one study).

It is usually caused by allergies or viral infections, often inciting excessive eye rubbing. Chemosis is also included in the Chandler Classification system of orbital infections.

If chemosis has occurred due to excessive rubbing of the eye, the first aid to be given is a cold water wash for eyes.

Other causes of chemosis include:

- Superior vena cava obstruction, accompanied by facial oedema

- Hyperthyroidism, associated with exophthalmos, periorbital puffiness, lid retraction, and lid lag

- Cavernous sinus thrombosis, associated with infection of the paranasal sinuses, proptosis, periorbital oedema, retinal haemorrhages, papilledema, extraocular movement abnormalities, and trigeminal nerve sensory loss

- Carotid-cavernous fistula - classic triad of chemosis, pulsatile proptosis, and ocular bruit

- Cluster headache

- Trichinellosis

- Systemic lupus erythematosus (SLE)

- Angioedema

- Acute glaucoma

- Panophthalmitis

- Orbital cellulitis

- Gonorrheal conjunctivitis

- Dacryocystitis

- Spitting cobra venom to the eye

- High concentrations of phenacyl chloride in chemical mace spray

- Urticaria

- Trauma

- Post surgical

- Rhabdomyosarcoma of the orbit

A large number of conditions may cause symptoms and signs similar to diabetic myonecrosis and include: deep vein thrombosis, thrombophlebitis, cellulitis, fasciitis, abscess, haematoma, myositis, pseudothrombophlebitis (ruptured synovial cyst), pyomyositis, parasitic myositis, osteomyelitis, calcific myonecrosis, myositis ossificans, diabetic myotrophy, muscle strain or rupture, bursitis, vasculitis, arterial occlusion, haemangioma, lymphoedema, sarcoidosis, tuberculosis, cat-scratch disease, amyloidosis, as well as tumours of lipoma, chondroma, fibroma, leiomyoma and sarcoma.

The adenoids, like all lymphoid tissue, enlarge when infected. Although lymphoid tissue does act to fight infection, sometimes bacteria and viruses can lodge within it and survive. Chronic infection, either viral or bacterial, can keep the pad of adenoids enlarged for years, even into adulthood. Some viruses, such as the Epstein-Barr Virus, can cause dramatic enlargement of lymphoid tissue. Primary or reactivation infections with Epstein Barr Virus, and certain other bacteria and viruses, can even cause enlargement of the adenoidal pad in an adult whose adenoids had previously become atrophied.

The cause of PVS is unknown; however, genetic factors and nutritional deficiencies may play a role. It is more common in women, particularly in middle age (peak age is over 50). In these patients, esophageal squamous cell carcinoma risk is increased; therefore, it is considered a premalignant process.

The condition is associated with koilonychia, glossitis, inflammation of the lips (cheilitis), and splenomegaly.

Esophageal web in Plummer-Vinson syndrome is found at upper end of esophagus(post cricoid region) and Schatzki ring may be found at the lower end of esophagus.

Treatment is first with many different high-dose steroids, namely glucocorticoids. Then, if symptoms do not improve additional immunosuppression such as cyclophosphamide are added to decrease the immune system's attack on the body's own tissues. Cerebral vasculitis is a very rare condition that is difficult to diagnose, and as a result there are significant variations in the way it is diagnosed and treated.

People with HPV-mediated oropharyngeal cancer tend to have higher survival rates. The prognosis for people with oropharyngeal cancer depends on the age and health of the person and the stage of the disease. It is important for people with oropharyngeal cancer to have follow-up exams for the rest of their lives, as cancer can occur in nearby areas. In addition, it is important to eliminate risk factors such as smoking and drinking alcohol, which increase the risk for second cancers.

"Primary" Central Nervous System (CNS) vasculitis is said to be present if there is no underlying cause. The exact mechanism of the primary disease is unknown, but the fundamental mechanism of all vasculitides is auto-immune. Other possible causes of cerebral vasculitis are infections, systemic auto-immune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis, medications and drugs (amphetamine, cocaine and heroin), some forms of cancer (lymphomas, leukemia and lung cancer) and other forms of systemic vasculitis such as granulomatosis with polyangiitis, polyarteritis nodosa or Behçet's disease. It may imitate, and is in turn imitated by, a number of other diseases that affect the blood vessels of the brain diffusely such as fibromuscular dysplasia and thrombotic thrombocytopenic purpura.

Choking is the fourth most common cause of unintentional injury-related death in the US. Many episodes are not reported because they are brief and resolve without seeking medical attention. Among reported events, the majority of episodes (80%) occur among children younger than age 15, with fewer episodes (20%) among age 15 and older. The death rate from choking is low at most ages but increases starting around age 74. Choking due to a foreign object resulted in 162,000 deaths (2.5 per 100,000) in 2013, compared to 140,000 deaths (2.9 per 100,000) in 1990.

There is risk of perforation of the esophagus with the use of dilators for treatment. Furthermore, it is one of the risk factors for developing squamous cell carcinoma of the oral cavity, esophagus, and hypopharynx.

There is some low quality evidence suggesting that mometasone may lead to symptomatic improvement in children with adenoid hypertrophy.

Surgical removal of the adenoids is a procedure called adenoidectomy. Carried out through the mouth under a general anaesthetic, adenoidectomy involves the adenoids being curetted, cauterised, lasered, or otherwise ablated. Adenoidectomy is most often performed because of nasal obstruction, but is also performed to reduce middle ear infections and fluid (otitis media). The procedure is often carried out at the same time as a tonsillectomy, since the adenoids can be clearly seen and assessed by the surgeon at that time.

Chemosis is the swelling (or edema) of the conjunctiva. It is due to the oozing of exudate from abnormally permeable capillaries. In general, chemosis is a nonspecific sign of eye irritation. The outer surface covering appears to have fluid in it. The conjunctiva becomes swollen and gelatinous in appearance. Often, the eye area swells so much that the eyes become difficult or impossible to close fully. Sometimes, it may also appear as if the eyeball has moved slightly backwards from the white part of the eye due to the fluid filled in the conjunctiva all over the eyes except the iris. The iris is not covered by this fluid and so it appears to be moved slightly inwards.

Otitis media is a particularly common cause of otalgia in early childhood, often occurring secondary to other infectious illnesses, such as colds, coughs, or conjunctivitis.

Choking is caused by an object from outside the body, also called a foreign body, blocking the airway. The object can block the upper or lower airway passages. The airway obstruction is usually partial but can also be complete.

Among children, the most common causes of choking are food, coins, toys, and balloons. In one study, peanuts were the most common object found in the airway of children evaluated for suspected foreign body aspiration. Foods that pose a high risk of choking include hot dogs, hard candy, nuts, seeds, whole grapes, raw carrots, apples, popcorn, peanut butter, marshmallows, chewing gum, and sausages. The most common cause of choking death in children is latex balloons. Small, round non-food objects such as balls, marbles, toys, and toy parts are also associated with a high risk of choking death because of their potential to completely block a child's airway.

Children younger than age three are especially at risk of choking because they explore the environment by putting objects in their mouth. Also, young children are still developing the ability to chew food completely. Molar teeth, which come in around 1.5 years of age, are necessary for grinding food. Even after molar teeth are present, children continue developing the ability to chew food completely and swallow throughout early childhood. In addition, a child's airway is smaller in diameter than an adult's airway, which means that smaller objects can cause an airway obstruction in children. Infants and young children generate a less forceful cough than adults, so coughing may not be as effective in relieving an airway obstruction. Finally, children with neuromuscular disorders, developmental delay, traumatic brain injury, and other conditions that affect swallowing are at an increased risk of choking.

In adults, choking often involves food blocking the airway. Risk factors include using alcohol or sedatives, undergoing a procedure involving the oral cavity or pharynx, wearing oral appliances, or having a medical condition that causes difficulty swallowing or impairs the cough reflex. Conditions that can cause difficulty swallowing and/or impaired coughing include neurologic conditions such as strokes, Alzheimer disease, or Parkinson disease. In older adults, risk factors also include living alone, wearing dentures, and having difficulty swallowing.

Children and adults with neurologic, cognitive, or psychiatric disorders may experience a delay in diagnosis because there may not be a known history of a foreign body entering the airway.

The risk factors that can increase the risk of developing oropharyngeal cancer are:

- Smoking and chewing tobacco

- Heavy alcohol use

- A diet low in fruits and vegetables

- Chewing betel quid, a stimulant commonly used in parts of Asia

- Mucosal infection with human papilloma virus (HPV) (HPV-mediated oropharyngeal cancer)

- HPV infection

- Plummer-Vinson syndrome

- Poor nutrition

- Asbestos exposure

Certain genetic changes including: P53 mutation and CDKN2A (p16) mutations.

High-risk lesions:

- Erythroplakia

- Speckled erythroplakia

- Chronic hyperplastic candidiasis

Medium-risk lesions:

- Oral submucosal fibrosis

- Syphilitic glossitis

- Sideropenic dysphagia (or Paterson-Kelly-Brown syndrome)

Low-risk lesions:

- Oral lichen planus

- Discoid lupus erythematosus

- Discoid keratosis congenita

The lower respiratory tract consists of the trachea (wind pipe), bronchial tubes, the bronchioles, and the lungs.

Lower respiratory tract infections are generally more serious than upper respiratory infections. LRIs are the leading cause of death among all infectious diseases. The two most common LRIs are bronchitis and pneumonia. Influenza affects both the upper and lower respiratory tracts, but more dangerous strains such as the highly pernicious H5N1 tend to bind to receptors deep in the lungs.