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Nontoxic diffuse goitre
Nontoxic diffuse goitre (ICD-11 5A01.0, ICD-10 E04.0) is diffuse thyroid enlargement from follicular multiplication with normal thyroid function, no hyperthyroidism; precursor of nodular goitre.
Nontoxic multinodular goitre
Nontoxic multinodular goitre (ICD-11 5A01.2, ICD-10 E04.2) is a thyroid with multiple nodules from follicular multiplication and normal hormone function; managed by observation, surgery, or radioiodine, unlike its toxic counterpart.
Nontoxic single thyroid nodule
Nontoxic single thyroid nodule (ICD-11 5A01.1; ICD-10 E04.1): a solitary euthyroid thyroid nodule without hyperthyroidism, usually benign, evaluated by TSH, ultrasound risk stratification, and selective FNA.
Nonunion after arthrodesis
Nonunion after arthrodesis (pseudarthrosis after fusion, ICD-11 FC01.7) is failed bony union of a surgically fused joint; pooled foot and ankle rate 8.1%, tibiotalocalcaneal 27.1%, smoking a key risk factor.
Nonunion of fracture
Nonunion of fracture (pseudarthrosis, ICD-11 FB80.8): failure of a broken bone to heal, FDA-defined as 9 months since injury with no healing progress for 3 months; affects 5-10% of acute fractures, most often the tibia, treated by fixation revision and bone grafting.
Nonverbal learning disorder
Nonverbal learning disorder (NVLD), or developmental visuospatial disorder, is a proposed neurodevelopmental condition of visual-spatial processing deficits with preserved verbal skills; not in DSM-5, affecting an estimated 2.2 to 2.9 million North American children.
Noonan syndrome with multiple lentigines
Noonan syndrome with multiple lentigines (NSML), formerly LEOPARD syndrome, is a rare autosomal dominant RASopathy caused by PTPN11 (~85%), RAF1, BRAF, or MAP2K1 variants, marked by lentigines, hypertrophic cardiomyopathy, short stature, and distinctive facies.
Noonan syndrome-like disorder with juvenile myelomonocytic leukemia
Noonan syndrome-like disorder with juvenile myelomonocytic leukemia, also called CBL syndrome, is a rare autosomal dominant RASopathy caused by germline CBL mutations at 11q23.3, combining Noonan-like features with JMML predisposition that often regresses spontaneously.
Noonan syndrome-like disorder with loose anagen hair
Noonan syndrome-like disorder with loose anagen hair (NS/LAH, Mazzanti syndrome) is a rare autosomal dominant RASopathy caused by SHOC2 or PPP1CB variants, combining Noonan-type features with easily plucked anagen hair, heart defects, and short stature.
Nootropic
Nootropics, also called smart drugs or cognition enhancers, are substances meant to improve memory, attention, and learning; the term was coined in 1972, and evidence of benefit in healthy adults is weak.
Noradrenergic neuron
A noradrenergic neuron is a neuron that synthesizes and releases norepinephrine (noradrenaline), a neurotransmitter governing arousal, attention, and stress; the largest cluster sits in the brainstem's locus coeruleus.
NORCCAP trial
NORCCAP (Norwegian Colorectal Cancer Prevention) trial: Norwegian population-registry RCT, 1999-2001, testing once-only flexible sigmoidoscopy with or without FIT in 100,210 people aged 50-64; no incidence reduction at 7 years, mortality benefit emerging after about 9.5 years.
Norelgestromin
Norelgestromin (NGMN), the primary active metabolite of norgestimate, is the progestin in the once-weekly contraceptive patch Ortho Evra/Evra/Xulane, delivering 150 mcg NGMN plus ethinyl estradiol; efficacy matches oral contraceptives with better compliance.
Norepinephrine–dopamine reuptake inhibitor
Norepinephrine–dopamine reuptake inhibitor (NDRI): antidepressant class blocking NET and DAT without serotonergic activity; bupropion (Wellbutrin, Zyban) is the principal drug, FDA-approved 1989 for depression and 1997 for smoking cessation.
Norethisterone
Norethisterone (norethindrone), 19-nor-17α-ethynyltestosterone, is a synthetic progestogen synthesized at Syntex, Mexico City, in 1951; used in progestin-only pills (350 μg), injectable oenanthate, and menstrual disorder therapy.
Norfloxacin
Norfloxacin (NFLX) is the first fluoroquinolone antibiotic, discovered in 1977 at Kyorin Pharmaceutical with fluorine at position 6 and piperazine at position 7; marketed 1986, it treats urinary tract infections via DNA gyrase inhibition and is 10x more active than nalidixic acid.
Norgestimate
Norgestimate (NGM), a 19-norsteroid progestin prodrug converted to norelgestromin, is used with ethinyl estradiol in combined oral contraceptives such as Ortho Tri-Cyclen, FDA-approved since 1989 for pregnancy prevention and moderate acne, with levonorgestrel-level VTE risk.
Norma M. Lang
Norma M. Lang is an American nurse scientist known for creating standardized measures of nursing care quality, and Dean Emerita of the University of Pennsylvania School of Nursing.
Normal electroretinogram
Normal electroretinogram: retinal electrical response to light within age- and electrode-specific reference limits under ISCEV standard dark- and light-adapted full-field or pattern ERG protocols.
Normal pressure hydrocephalus
Normal pressure hydrocephalus (NPH, iNPH, Hakim-Adams syndrome) is an adult disorder with enlarged ventricles, normal CSF pressure, and the triad of gait apraxia, urinary incontinence, and dementia; treatable by ventriculoperitoneal shunt.
Normal tension glaucoma
Normal tension glaucoma (NTG), or low-tension glaucoma, is open-angle glaucoma with IOP always ≤21 mmHg; 30–40% of OAG cases, common in Asia (up to 92% in Japan), treated by IOP reduction despite normal pressures.
Normal tissue complication probability model
The normal tissue complication probability (NTCP) model is a mathematical model in radiation oncology that converts the radiation dose to a healthy organ into an estimated complication risk.
Norman Bethune
Norman Bethune (白求恩, Bai Qiu'en), 1890-1939, Canadian thoracic surgeon and Communist activist; pioneered mobile front-line blood transfusion in the Spanish Civil War and served Mao's 8th Route Army, dying of septicaemia in Hebei, China, a national hero.
Norman F. Gant
Norman F. Gant, also known as Norman F. Gant Jr., is an American obstetrician-gynecologist at UT Southwestern known for the angiotensin II pressor-response test in pregnancy.
Norman G. Levinsky
Norman G. Levinsky was an American nephrologist at Boston University School of Medicine who chaired its Department of Medicine from 1972 to 1997 and wrote on Medicare and research ethics.
Normocytic anemia
Normocytic anemia: anemia with normal red cell size (MCV 80-100 fL), also called normochromic normocytic anemia; most often from anemia of chronic disease, renal failure, endocrine or marrow failure, or acute blood loss.
Normothermic regional perfusion
Normothermic regional perfusion (NRP) is a procurement technique in donation after circulatory death that restores oxygenated circulation to a deceased donor's abdominal organs, and sometimes the heart, using ECMO.
Norrie disease
Norrie disease, also called Norrie-Warburg or Anderson-Warburg syndrome, is a rare X-linked recessive disorder caused by NDP gene mutations, causing congenital blindness, retinal detachment, and often progressive hearing loss and developmental delay in boys.
North Carolina macular dystrophy
North Carolina macular dystrophy (NCMD, MCDR1, CAPED) is a rare non-progressive autosomal dominant congenital macular disorder with drusen and photoreceptor atrophy, caused by noncoding variants upstream of PRDM13 on 6q16 or at the MCDR3 locus on chromosome 5.
Nortriptyline
Nortriptyline, a tricyclic antidepressant and the principal active metabolite of amitriptyline (ATC N06AA10), treats depression, aids smoking cessation, and is used for neuropathic pain; metabolized by CYP2D6 with cardiac arrhythmia risk.