Here is the list of the most common diseases that begin with letter “O“:
- Obsessive–compulsive disorder (OCD)
- Obstructive sleep apnea (OSA)
- Ochoa syndrome
- Opportunistic infection
- Optic atrophy
- Osteoarthritis (OA)
- Ovarian cancer
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems. Body mass index (BMI), a measurement which compares weight and height, defines people as overweight (pre-obese) if their BMI is between 25 kg/m2 and 30 kg/m2, and obese when it is greater than 30 kg/m2.
Obesity increases the likelihood of various diseases, particularly heart disease, type 2 diabetes, breathing difficulties during sleep, certain types of cancer, and osteoarthritis. Obesity is most commonly caused by a combination of excessive dietary calories, lack of physical activity, and genetic susceptibility, although a few cases are caused primarily by genes, endocrine disorders, medications or psychiatric illness. Evidence to support the view that some obese people eat little yet gain weight due to a slow metabolism is limited; on average obese people have a greater energy expenditure than their thin counterparts due to the energy required to maintain an increased body mass.
Dieting and physical exercise are the mainstays of treatment for obesity. Moreover, it is important to improve diet quality by reducing the consumption of energy-dense foods such as those high in fat and sugars, and by increasing the intake of dietary fiber. To supplement this, or in case of failure, anti-obesity drugs may be taken to reduce appetite or inhibit fat absorption. In severe cases, surgery is performed or an intragastric balloon is placed to reduce stomach volume and/or bowel length, leading to earlier satiation and reduced ability to absorb nutrients from food.
Obesity is a leading preventable cause of death worldwide, with increasing prevalence in adults and children, and authorities view it as one of the most serious public health problems of the 21st century.
Obsessive–compulsive disorder (OCD) is an anxiety disorder characterized by intrusive thoughts that produce uneasiness, apprehension, fear, or worry, by repetitive behaviors aimed at reducing anxiety, or by a combination of such thoughts (obsessions) and behaviors (compulsions). Symptoms may include repetitive handwashing; extensive hoarding; preoccupation with sexual or aggressive impulses, or with particular religious beliefs; aversion to odd numbers; and nervous habits, such as opening a door and closing it a certain number of times before one enters or leaves a room. These symptoms can be alienating and time-consuming, and often cause severe emotional and financial distress. The acts of those who have OCD may appear paranoid and come across to others as psychotic. However, OCD sufferers generally recognize their thoughts and subsequent actions as irrational, and they may become further distressed by this realization.
OCD is the fourth-most-common mental disorder, and is diagnosed nearly as often as asthma and diabetes mellitus. In the United States, one in 50 adults has OCD. Obsessive–compulsive disorder affects children and adolescents as well as adults. Roughly one third to one half of adults with OCD report a childhood onset of the disorder, suggesting the continuum of anxiety disorders across the life span. The phrase “obsessive–compulsive” has become part of the English lexicon, and is often used in an informal or caricatured manner to describe someone who is meticulous, perfectionistic, absorbed in a cause, or otherwise fixated on something or someone. Although these signs may be present in OCD, a person who exhibits them does not necessarily have OCD, and may instead have obsessive–compulsive personality disorder (OCPD), an autism spectrum disorder, or no clinical condition. Multiple psychological and biological factors may be involved in causing obsessive–compulsive syndromes.
Obstructive sleep apnea (OSA) or obstructive sleep apnea syndrome is the most common type of sleep apnea and is caused by obstruction of the upper airway. It is characterized by repetitive pauses in breathing during sleep, despite the effort to breathe, and is usually associated with a reduction in blood oxygen saturation. These pauses in breathing, called apneas (literally, “without breath”), typically last 20 to 40 seconds. The individual with OSA is rarely aware of having difficulty breathing, even upon awakening. It is recognized as a problem by others witnessing the individual during episodes or is suspected because of its effects on the body (sequelae). OSA is commonly accompanied with snoring.
Symptoms may be present for years, even decades without identification, during which time the sufferer may become conditioned to the daytime sleepiness and fatigue associated with significant levels of sleep disturbance. Persons who sleep alone without a long-term human partner may not be told about their sleep disorder symptoms.
Since the muscle tone of the body ordinarily relaxes during sleep, and since, at the level of the throat, the human airway is composed of walls of soft tissue, which can collapse, it is easy to understand how breathing can be obstructed during sleep. Although a very low level of obstructive sleep apnea is considered to be within the bounds of normal sleep, and many individuals experience episodes of obstructive sleep apnea at some point in life, a much smaller percentage of people are afflicted with chronic, severe obstructive sleep apnea.
Many people experience episodes of obstructive sleep apnea for only a short period of time. This can be the result of an upper respiratory infection that causes nasal congestion, along with swelling of the throat, or tonsillitis that temporarily produces very enlarged tonsils.
Ochoa syndrome, also called urofacial syndrome or hydronephrosis with peculiar facial expression, is an autosomal recessive congenital disorder characterized by inverted facial expressions in association with obstructive disease of the urinary tract. Infants with the disorder exhibit an inverted smile. They appear to be crying when they are actually smiling, in conjunction with uropathy. They also may be affected by hydronephrosis.
Ochronosis is the syndrome caused by the accumulation of homogentisic acid in connective tissues. The phenomenon was first described by Rudolf Virchow in 1865. The condition was named after the yellowish (ocher-like) discoloration of the tissue seen on microscopic examination. However, macroscopically the affected tissues appear bluish grey because of a light scattering phenomenon known as the Tyndall effect. The condition is most often associated with alkaptonuria but can occur from exogenous administration of phenol complexes like hydroquinone.
Ochronosis occurs because of deposition of phenols (such as homogenistic acid and hydroquinone) as plaques in the matrix of cartilage. The pigments can also be incorporated into collagen and elastin fibers. In the skin, the pigment alters the structure of the fibers causing enlargement and curling. They come to closely resemble fibers seen in biopsies of solar elastosis. The embedded pigments also form cross-linkages with pigment depositions in adjacent fibers, stabilizing and reducing the elastic recoil of the fibers. This results in hardening of elastic structures increasing their rigidity and brittleness.
Odontophobia or dental fear refers to the fear of dentistry and of receiving dental care. A severe form of this fear (specific phobia) is variously called dental phobia, dentophobia, dentist phobia, or dental anxiety. However, it has been suggested that the term “dental phobia” is often a misnomer, as many people with this condition do not feel their fears to be excessive or unreasonable and resemble individuals with post-traumatic stress disorder, caused by previous traumatic dental experiences.
It is estimated that as many as 75% of US adults experience some degree of dental fear, from mild to severe. Approximately 5 to 10 percent of U.S. adults are considered to experience dental phobia. That is, they are so fearful of receiving dental treatment that they avoid dental care at all costs. Many dentally fearful people will only seek dental care when they have a dental emergency, such as a toothache or dental abscess. People who are very fearful of dental care often experience a “cycle of avoidance,” in which they avoid dental care due to fear until they experience a dental emergency requiring invasive treatment, which can reinforce their fear of dentistry.
Women tend to report more dental fear than men, and younger people tend to report being more dentally fearful than older individuals. People tend to report being more fearful of more invasive procedures, such as oral surgery, than they are of less invasive treatment, such as professional dental cleanings, or prophylaxis.
Oikophobia, also ecophobia, is a term used in psychiatry to refer to an aversion to home surroundings. It can also be used more generally to mean an abnormal fear of the home, or of the contents of a house (“fear of household appliances, equipment, bathtubs, household chemicals, and other common objects in the home”). The term derives from the Greek words oikos, meaning household, house, or family, and phobia, meaning “fear”.
In 1808 the poet and essayist Robert Southey used the word to describe a desire (particularly by the English) to leave home and travel. Southey’s usage as a synonym for wanderlust was picked up by other nineteenth century writers. In a 2004 book, the word was adapted by the British philosopher Roger Scruton to mean “the repudiation of inheritance and home”. He argued that it is “a stage through which the adolescent mind normally passes”, but that it is a feature of some radical political impulses and ideologies which espouse xenophilia (preference for alien cultures).
Onchocerciasis, also known as river blindness and Robles’ Disease, is a parasitic disease caused by infection by Onchocerca volvulus, a nematode (roundworm). Onchocerciasis is the world’s second-leading infectious cause of blindness. It is not the nematode but its endosymbiont, Wolbachia pipientis, that causes the severe inflammatory response that leaves many blind. The parasite is transmitted to humans through the bite of a blackfly of the genus Simulium. The larval nematodes spread throughout the body. When the worms die their Wolbachia symbionts are released, triggering a host immune system response that causes intense itching and can destroy nearby tissue, such as the eye.
The vast majority of infections occur in sub-Saharan Africa, although cases have also been reported in Yemen and isolated areas of Central and South America. An estimated 18 million people suffer from onchocerciasis, with approximately 270,000 cases of blindness related to the infection.
Opportunistic infection is a general term for defining an infection caused by pathogens (bacterial, viral, fungal or protozoan) that usually do not cause disease in a healthy host, i.e. one with a healthy immune system. A compromised immune system, however, presents an “opportunity” for the pathogen to infect.
Optic atrophy is the loss of some or most of the fibers of the optic nerve. In medicine, “atrophy” usually means “shrunken but capable of regrowth”, so some argue that “optic atrophy” as a pathological term is somewhat misleading and use “optic neuropathy” instead. The optic nerve is part of the brain and has no capability for regeneration. Hence, there can be no recovery from optic atrophy and the term may refer to serious or mild, but always irreversible visual loss due to damage to the optic nerve. Three types of degeneration are seen: transsynaptic, anterograde, and retrograde.
There may be symptoms associated with loss of vision (although there may be a particular difficulty with colour vision). Bilateral Optic Atrophy: Loss of vision and discoloration of discs in both eyes. This is a genetic form and can be inherited. Symptoms will be extremely varied. Some people will have near to normal vision, whereas others will have very poor vision.
Osteoarthritis (OA) also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion. A variety of causes—hereditary, developmental, metabolic, and mechanical—may initiate processes leading to loss of cartilage. When bone surfaces become less well protected by cartilage, bone may be exposed and damaged. As a result of decreased movement secondary to pain, regional muscles may atrophy, and ligaments may become more lax.
Treatment generally involves a combination of exercise, lifestyle modification, and analgesics. If pain becomes debilitating, joint replacement surgery may be used to improve the quality of life. OA is the most common form of arthritis, and the leading cause of chronic disability in the United States. It affects about 8 million people in the United Kingdom and nearly 27 million people in the United States.
The main symptom is pain, causing loss of ability and often stiffness. “Pain” is generally described as a sharp ache, or a burning sensation in the associate muscles and tendons. OA can cause a crackling noise (called “crepitus”) when the affected joint is moved or touched, and patients may experience muscle spasm and contractions in the tendons. Occasionally, the joints may also be filled with fluid. Humid and cold weather increases the pain in many patients.
OA commonly affects the hands, feet, spine, and the large weight bearing joints, such as the hips and knees, although in theory, any joint in the body can be affected. As OA progresses, the affected joints appear larger, are stiff and painful, and usually feel worse, the more they are used throughout the day, thus distinguishing it from rheumatoid arthritis.
Exercise, including running in the absence of injury, has not been found to increase one’s risk of developing osteoarthritis. Some investigators believe that mechanical stress on joints underlies all osteoarthritis, with many and varied sources of mechanical stress, including misalignments of bones caused by congenital or pathogenic causes; mechanical injury; overweight; loss of strength in muscles supporting joints; and impairment of peripheral nerves, leading to sudden or uncoordinated movements that overstress joints.
Osteochondritis is a painful type of osteochondrosis where the cartilage or bone in a joint is inflamed. It often refers to osteochondritis dissecans (sometimes spelled dessecans, and abbreviated OCD). The term dissecans refers to the “creation of a flap of cartilage that further dissects away from its underlying subchondral attachments (dissecans)”.
Osteochondroma is a type of benign tumor that consists of cartilage and bone. It is a benign capped-cartilage outgrowth, connected to bone by a stalk. It is the most frequently observed neoplasm of the skeleton. They generally occur at the end of the growth plates of long bones, often at joints. They most commonly form at the shoulder or the knee but have been known to occur in the long bones of the forearm (i.e. the radius and ulna).
Osteochondroma is a benign tumor that contains both bone and cartilage and usually occurs near the end of a long bone. This tumor, one of the most common benign bone tumors, takes the form of a cartilage-capped bony spur or outgrowth on the surface of the bone. It is sometimes referred to as osteocartilaginous exostosis.
Osteomalacia is the softening of the bones due to defective bone mineralization secondary to inadequate amounts of available phosphorus and calcium. Osteomalacia in children is known as rickets, and because of this, use of the term osteomalacia is often restricted to the milder, adult form of the disease. It may show signs as diffuse body pains, muscle weakness, and fragility of the bones. The most common cause of the disease is a deficiency in vitamin D, which is normally obtained from the diet and/or sunlight exposure.
Osteomalacia is a generalized bone condition in which there is inadequate mineralization of the bone. Many of the effects of the disease overlap with the more common osteoporosis, but the two diseases are significantly different. There are two main causes of osteomalacia: (1) insufficient calcium absorption from the intestine because of lack of dietary calcium or a deficiency of or resistance to the action of vitamin D; and (2) Phosphate deficiency caused by increased renal losses.
Osteomyelitis simply means an infection of the bone or bone marrow. It can be usefully subclassified on the basis of the causative organism (pyogenic bacteria or mycobacteria), the route, duration and anatomic location of the infection. In general, microorganisms may infect bone through one or more of three basic methods: via the bloodstream, contiguously from local areas of infection (as in cellulitis), or penetrating trauma, including iatrogenic causes such as joint replacements or internal fixation of fractures or root-canaled teeth. Once the bone is infected, leukocytes enter the infected area, and, in their attempt to engulf the infectious organisms, release enzymes that lyse the bone. Pus spreads into the bone’s blood vessels, impairing their flow, and areas of devitalized infected bone, known as sequestra, form the basis of a chronic infection.
Osteopetrosis, literally “stone bone”, also known as marble bone disease and Albers-Schonberg disease is an extremely rare inherited disorder whereby the bones harden, becoming denser, in contrast to more prevalent conditions like osteoporosis, in which the bones become less dense and more brittle, or osteomalacia, in which the bones soften.
Despite this excess bone formation, people with osteopetrosis tend to have bones that are more brittle than normal. Mild osteopetrosis may cause no symptoms, and present no problems. However, serious forms can result in stunted growth, deformity, increased likelihood of fractures, also patients suffers anemia, recurrent infections and hepatosplenomegaly due to bone expansion leading to bone marrow narrowing and extramedullary hematopoiesis. It can also result in blindness, facial paralysis, and deafness, due to the increased pressure put on the nerves by the extra bone.
Osteoporosis is a disease of bones that leads to an increased risk of fracture. In osteoporosis the bone mineral density (BMD) is reduced, bone microarchitecture is deteriorating, and the amount and variety of proteins in bone is altered. Osteoporosis is defined by the World Health Organization (WHO) as a bone mineral density that is 2.5 standard deviations or more below the mean peak bone mass (average of young, healthy adults) as measured by DXA; the term “established osteoporosis” includes the presence of a fragility fracture. The disease may be classified as primary type 1, primary type 2, or secondary. The form of osteoporosis most common in women after menopause is referred to as primary type 1 or postmenopausal osteoporosis. Primary type 2 osteoporosis or senile osteoporosis occurs after age 75 and is seen in both females and males at a ratio of 2:1. Finally, secondary osteoporosis may arise at any age and affects men and women equally. This form of osteoporosis results from chronic predisposing medical problems or disease, or prolonged use of medications such as glucocorticoids, when the disease is called steroid- or glucocorticoid-induced osteoporosis (SIOP or GIOP).
Osteoporosis risks can be reduced with lifestyle changes and sometimes medication; in people with osteoporosis, treatment may involve both. Lifestyle change includes diet and exercise, and preventing falls. Medication includes calcium, vitamin D, bisphosphonates and several others. Fall-prevention advice includes exercise to tone deambulatory muscles, proprioception-improvement exercises; equilibrium therapies may be included. Exercise with its anabolic effect, may at the same time stop or reverse osteoporosis. Osteoporosis is a component of the frailty syndrome.
Osteosclerosis, an elevation in bone density, is normally detected on an X-ray as an area of whiteness, and is where the bone density has significantly increased. Localized osteosclerosis can be caused by injuries that compress the bone, by osteoarthritis, and osteoma.
Otosclerosis is an abnormal growth of bone near the middle ear. It can result in hearing loss. Otosclerosis can result in conductive and/or sensorineural hearing loss. The primary form of hearing loss in otosclerosis is conductive hearing loss (CHL) whereby sounds reach the ear drum but is incompletely transferred via the ossicular chain in the middle ear, and thus partly fails to reach the inner ear (cochlea). This usually will begin in one ear but will eventually affect both ears with a variable course. On audiometry, the hearing loss is characteristically low-frequency, with higher frequencies being affected later. Sensorineural hearing loss (SNHL) has also been noted in patients with otosclerosis; this is usually a high-frequency loss, and usually manifests late in the disease. The causal link between otosclerosis and SNHL remains controversial.
Treatment of otosclerosis relies on two primary options: hearing aids (more recently including bone-conduction hearing aids) and a surgery called a stapedectomy. Hearing aids are usually very effective early in the course of the disease, but eventually a stapedectomy (or more frequently a variant called the stapedotomy) may be required for definitive treatment. Early attempts at hearing restoration via the simple freeing the stapes from its sclerotic attachments to the oval window were met with temporary improvement in hearing, but the conductive hearing loss would almost always recur. A stapedectomy consists of removing a portion of the sclerotic stapes footplate and replacing it with an implant that is secured to the incus. This procedure restores continuity of ossicular movement and allows transmission of sound waves from the eardrum to the inner ear. A modern variant of this surgery called a stapedotomy, is performed by drilling a small hole in the stapes footplate with a micro-drill or a laser, and the insertion of a piston-like prothesis.
Ovarian cancer is a cancerous growth arising from different parts of the ovary. Most (>90%) ovarian cancers are classified as “epithelial” and were believed to arise from the surface (epithelium) of the ovary. However, recent evidence suggests that the Fallopian tube could also be the source of some ovarian cancers. Since the ovaries and tubes are closely related to each other, it is hypothesized that these cells can mimic ovarian cancer. Other types arise from the egg cells (germ cell tumor) or supporting cells (sex cord/stromal).
In 2004, in the United States, 25,580 new cases were diagnosed and 16,090 women died of ovarian cancer. The risk increases with age and decreases with pregnancy. Lifetime risk is about 1.6%, but women with affected first-degree relatives have a 5% risk. Women with a mutated BRCA1 or BRCA2 gene carry a risk between 25% and 60% depending on the specific mutation. Ovarian cancer is the fifth leading cause of death from cancer in women and the leading cause of death from gynecological cancer. In early stages ovarian cancer is associated with abdominal distension. 10-year relative survival ranges from 84.1% in stage IA to 10.4% in stage IIIC.
Ovarian cancer causes non-specific symptoms. Early diagnosis would result in better survival, on the assumption that stage I and II cancers progress to stage III and IV cancers (but this has not been proven). Most women with ovarian cancer report one or more symptoms such as abdominal pain or discomfort, an abdominal mass, bloating, back pain, urinary urgency, constipation, tiredness and a range of other non-specific symptoms, as well as more specific symptoms such as pelvic pain, abnormal vaginal bleeding or involuntary weight loss. There can be a build-up of fluid (ascites) in the abdominal cavity.
Diagnosis of ovarian cancer starts with a physical examination (including a pelvic examination), a blood test (for CA-125 and sometimes other markers), and transvaginal ultrasound. The diagnosis must be confirmed with surgery to inspect the abdominal cavity, take biopsies (tissue samples for microscopic analysis) and look for cancer cells in the abdominal fluid. Treatment usually involves chemotherapy and surgery, and sometimes radiotherapy. In most cases, the cause of ovarian cancer remains unknown. Older women, and in those who have a first or second degree relative with the disease, have an increased risk.