O

O


Ober’s test see test, Ober’s


obese an adult who is more than 20% heavier than their height related ideal weight, with a body mass index of >25 and/or having a waist measurement of >1m; obesity correlates with risk of heart disease, hypertension, respiratory distress, type 2 diabetes mellitus, osteoarthritis and plantar fasciitis, see body: mass index


morbidly obese; morbid obesity an adult with BMI >30

objective signs measured physiological and/or pathological parameters recorded during patient examination


obligate aerobe microorganism that cannot survive in conditions of low oxygen tension


obligate anaerobe microorganism that cannot survive in normal oxygen levels


oblique slanted, i.e. non-perpendicular or non-horizontal, and non-parallel to the cardinal body planes


obliteration loss of a space or lumen, due to fibrosis, sclerosis or inflammation


obstruction occlusion; stenosis


occlusive arterial disease limb artery occlusion, due to progressive atherosclerosis and/or thrombosis, leading ultimately to distal tissue infarction


occlusive dressings topical agents that prevent surface evaporation of sweat, e.g. flexible collodion; Op-site spray. Tegaderm and Op-site films


occlusive wound dressing dressing excluding air from and preventing gaseous exchange at the wound surface; contraindicated on wounds that may harbour infection


occult spina bifida mild form of spina bifida, characterized by pes cavus, mild vertebral malformation at base of spine, but no spinal cord involvement


OCH-A-DRARR mnemonic for treatment of localized infection; see Table S3


oedema accumulation of excess tissue fluid in distal limb tissues associated with e.g. local inflammation/infection, abnormal lymphatic drainage, abdominal mass or cardiac/lung/renal dysfunction (Table O1)


anaphylactic oedema generalized swelling of facial skin and mucous membranes with associated difficulty in breathing and profound drop in blood pressure; characteristic of anaphylaxis (see anaphylaxis)

cardiac oedema peripheral oedema due to congestive heart failure

joint oedema oedema of joint soft tissues, due to joint (e.g. rheumatoid or osteoarthritis) or ligamentous inflammation (e.g. mechanical trauma, joint strain/sprain)

non-pitting oedema indurated and firm oedematous lower-limb tissues; indicative of long-standing oedema and fibrosis, e.g. in long-term venous incompetence

peripheral oedema oedema of distal (foot and limb) tissues secondary to e.g. cardiac, pulmonary or renal dysfunction, venous dysfunction, abdominal mass or hypertension

pitting oedema relatively soft, tissue oedema affecting both feet and lower legs or unilateral swelling of a limb with incompetent venous return; characterized by retention of the depression caused by fingertip pressure

pulmonary oedema lung oedema due to heart valve dysfunction

Table O1 Presentations of oedema in the lower limb


















Oedema type Cause
Unilateral Within the limb
Local, e.g. as the result of local trauma, inflammation or infection
Regional, e.g. as the result of proximal limb trauma, inflammation, infection or venous compromise
Bilateral Systemic disease (e.g. heart disease, renal dysfunction, abdominal mass, hypertension, lung dysfunction)
Pitting Systemic disease (e.g. heart disease; hypertension; venous compromise)
Indurated/non-pitting Long-standing oedema (e.g. marked venous compromise; subsequent to deep-vein thrombosis)

oestradiol steroid hormone, similar to oestrogen; secreted by the ovary, testes, placenta and adrenal cortex


oestrogen natural or synthetic substances that induce development of secondary sexual characteristics, growth and maturation of long bones during youth; used therapeutically to treat carcinoma of breast and prostate


oil drop sign see sign, oil drop


ointment see Table V1


oligodactyly congenital absence or underdevelopment of part or all of one or more digits, with or without associated metatarsal absence


-oma denoting neoplasm


omega nail see nail, involuted


omeprazole (Losec) see proton pump inhibitors


oncogene viral gene (e.g. in certain retroviruses) inducing host cell neoplasia


oncotic pressure osmotic pressure exerted by plasma proteins in blood


‘onion bulb’ nerves Schwann cell morphology characteristic of nerves in hereditary sensorimotor neuropathies


onych-; onycho- denoting nail tissue (see leukonychia; nail)


onychatrophia; anonychia permanent loss of nail unit, due to matrix atrophy, e.g. in lichen planus, severe psoriasis and dermal pathologies characterized by fibrosis or scar formation


onychauxis nail plate hypertrophy without distortion


onychia acute or chronic inflammation of nail unit; associated with bacterial infection of nail bed and/or matrix and resultant nail plate dystrophy; see paronychia


onychia of nail macro-onychia abnormally large or conjoined nails, characteristic of total syndactyly, e.g. Apert’s syndrome


micro-onychia abnormally small nails, e.g. scleroderma

trachyonychia; twenty-nail dystrophy excessive ridging and roughness of all nail plates with dorsal flattening or convexity, associated with lichen planus, psoriasis and alopecia areata

Onychocil proprietary paint containing salicylic and other acids, used as topical treatment for mild onychomycosis


onychocryptosis see ingrowing toenail


onychodermal band; Terry’s onychodermal band fine, pallid, translucent band at the junction of the distal nail bed and hyponychium


onychodystrophy nail plate dystrophy due to congenital defect, or recent illness, inflammation or injury


onychogryphosis; ostler’s nail; ram’s horn nail gross thickness with overall nail plate deformity


onycholysis idiopathic, systemic, dermatopathology or trauma-induced separation of all or part of one or more nail plates from the distal nail bed; associated with hyperhidrosis, thyrotoxicosis, psoriasis, fungal infection, local pressure and drug therapy (see photo-onycholysis)


onychomadesis; onychoptosis; aplastic anonychia separation of the nail plate from the proximal nail bed ± transient arrest of nail growth and Beau’s line formation; occurs secondary to local trauma (e.g. subungual haematoma), dermatopathologies characterized by matrix scarring, local inflammation or infection, peripheral vascular disease, severe Raynaud’s, or as a familial trait


onychomalacia abnormal nail plate softness, e.g. due to immersion and/or detergents


onychomycosis fungal infection of the nail unit, due to Trichophyton rubrum or T. mentagrophytes infection; characterized by nail plate thickening and dystrophy, white/yellow/brown discoloration, chalkiness, friability and splitting, and a musty smell; treated by topical antifungal lacquers for 6 months or more, and/or systemic drugs such as terbinafine 250 mg daily for 12–16 weeks (Table O2 and see Table F13)


Table O2 Clinical presentations of onychomycosis
























Onychomycosis Feature
DLSO Distal and lateral subungual onychomycosis: commonest presentation of onychomycosis; hyponychium is infected by the fungus leading to hyperkeratosis of the distal nail bed; spreads proximally to cause hyperkeratosis of the proximal nail bed and onycholysis
SWO Superficial white onychomycosis: less common than DLSO; caused by infection with Trichophyton mentagrophytes; affecting the dorsal nail plate; may respond to topical treatments
PSO Proximal subungual onychomycosis: involvement of the proximal nail bed, spreading distally; due to infection with Candida sp., T. rubrum and Scropulariopsis brevicaulis
TDO Total dystrophic onychomycosis: the end result of untreated DLSO, SWO or PSO
CO Candidal onychomycosis: nail involvement due to local spread from a chronic paronychia (typical of patients whose hands are habitually wet), distal nail plate infection (rare – mainly affecting patients with Raynaud’s), chronic mucocutaneous candidiasis (due to an inborn defect of cell-mediated immunity) or due to opportunist yeast infection of psoriatic nails
EO Endonyx onychomycosis: a rare form of onychomycosis caused by infection with T. soudanense

onychophagia nail biting


onychophosis callosity or corn within the nail sulcus, associated with nail dystrophy, shoe trauma or biomechanical dysfunction


onychoptosis see onychomadesis


onychorrhexis exaggeration of the normal longitudinal ridge pattern and brittleness of nail plate; associated with lichen planus, rheumatoid arthritis and peripheral circulatory disorders


onychosicca nail plate atrophy and dryness; e.g. in the elderly


onychotillomania habitual biting or picking (i.e. self-harming) of the nail unit, characterized by central plate dystrophy (i.e. longitudinal band of transverse central ridges), discoloration and loss of central part of eponychium


open-chain motion non-weight-bearing movement of the foot and/or limb


open fracture see fracture, open Table C18


opiates morphine-derived drugs, e.g. codeine, diamorphine, used to control severe central and peripheral pain; induce narcosis, euphoria, constipation and cough reflex suppression; patients readily develop tolerance and habituate, requiring larger doses of opiate to achieve a therapeutic effect


opioid any non-morphine-derived narcotic drug, or naturally occurring substance with an opiate-like therapeutic action


opioid analgesics powerful analgesics which act on the central nervous system, e.g. codeine, morphine, fentanyl, tramadol, co-proxamol


opioid receptors specific cell surface receptors within the central and peripheral nervous system, which combine with naturally occurring opioid compounds (e.g. endorphins) to reduce pain and increase euphoria


Oppenheim response; Oppenheim reflex see response, Oppenheim


opportunistic pathogen microorganism causing infection in a host with lowered disease resistance (e.g. due to concomitant illness or drug therapy)


Opsite semipermeable adhesive film dressing (see Table D10); also used to control symptoms of diabetic hyperalgesia and neuropathic pain


opsonization addition of an opsonin (i.e. a complement moiety) to a bacterium, to ensure that the microorganism is readily identified, and more efficiently taken up, by macrophages


optimal analgesia use of pain-controlling agents (e.g. long-acting local anaesthetic agents, non-steroidal anti-inflammatory agents, opiates and other pain-modulating drug stratagems) to normalize postoperative and ongoing pain states


oral glucose tolerance test glucose tolerance test


oral hypoglycaemic drugs agents, e.g. biguanides, sulphonylureas, acarbose and glitazones, taken by mouth to treat diabetes mellitus, and achieve normoglycaemia


order biological classification, between ‘class’ and ‘family’


orf see disease, hand, foot and mouth


organelles specialized intracellular structures; e.g. mitochondria, Golgi apparatus, centrioles, granular and agranular endoplasmic reticulum, vacuoles, microsomes, lysosomes, plasma membrane and fibrils (Table O3)


Table O3 Cell organelles









Structure Characteristic
Cell membrane Bimolecular lipid and protein membrane that surrounds the cell
• Bi-layer of non-polar lipid molecules (phosphatidylcholine, phospharidylethanolamine, cholesterol) that acts as a barrier to water and hydrophilic solutes
• Proteins:
• Structural proteins

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