O
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
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)
Table O1 Presentations of oedema in the lower limb
| Oedema type | Cause |
|---|---|
| Unilateral | Within the limbLocal, e.g. as the result of local trauma, inflammation or infectionRegional, 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
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)
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
Onychocil proprietary paint containing salicylic and other acids, used as topical treatment for mild onychomycosis
onychocryptosis see ingrowing toenail
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 |
onychophosis callosity or corn within the nail sulcus, associated with nail dystrophy, shoe trauma or biomechanical dysfunction
onychoptosis see onychomadesis
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
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
Opsite semipermeable adhesive film dressing (see Table D10); also used to control symptoms of diabetic hyperalgesia and neuropathic pain
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)
| 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:
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