Nervous and sensory conditions

Neuropathic pain

Neuropathic pain: pain caused by a lesion or disease of the somatosensory nervous system (IASP definition). First-line drugs are TCAs, SNRIs, pregabalin, and gabapentin per NeuPSIG; opioids are third-line.

Neuroprotection

Neuroprotection is any strategy that interrupts or slows the biochemical events leading to irreversible death of nerve cells, studied in stroke, traumatic brain injury, and neurodegenerative disease.

Neuroretinitis

Neuroretinitis: inflammation of the optic nerve and peripapillary retina causing vision loss, disc swelling, and a macular star; most often caused by Bartonella henselae (cat-scratch disease), with about half of cases idiopathic.

Neurosarcoidosis

Neurosarcoidosis is nervous system involvement by sarcoidosis, affecting about 5% of sarcoidosis patients, most often with cranial neuropathy; treated with glucocorticoids plus methotrexate, azathioprine, or infliximab.

Neurotoxin

A neurotoxin, also known as a neurotoxicant, is a toxic substance of microbial, plant, or animal origin that interferes with nervous system function, including botulinum toxin and tetrodotoxin.

New-onset refractory status epilepticus

New-onset refractory status epilepticus (NORSE), including its subtype FIRES, is a clinical presentation of unexplained refractory status epilepticus in people without prior epilepsy, defined by 2018 consensus and managed per 2022 international recommendations.

Nicotine intoxication

Nicotine intoxication (ICD-11 6C4A.3), also called tobacco intoxication, is a transient toxic condition from nicotine exposure, with early stimulation then depression, vomiting, seizures, and possible cardiovascular collapse; no specific antidote exists.

Night terror

Night terror (sleep terror, pavor nocturnus): a non-REM parasomnia of screaming and thrashing from deep slow-wave sleep, mainly in children aged 3-10, with no morning recall, distinct from nightmares and sleep paralysis.

Nitrogen narcosis

Nitrogen narcosis, also called inert gas narcosis or the Martini effect, is reversible CNS impairment in divers breathing compressed air at depth; symptoms begin around 10-30 msw, resolve on ascent, and are prevented with helium-based gas mixtures.

NKX6-2-related autosomal recessive hypomyelinating leukodystrophy

NKX6-2-related autosomal recessive hypomyelinating leukodystrophy, also known as spastic ataxia 8 (SPAX8), is a rare genetic white-matter disease caused by NKX6-2 variants, ranging from severe infantile spasticity to later-onset ataxia.

Nodular neuronal heterotopia

Nodular neuronal heterotopia (periventricular nodular heterotopia, PNH) is a rare malformation of cortical development in which neurons fail to migrate, forming gray-matter nodules along the ventricles; causes include FLNA and ARFGEF2 mutations, with epilepsy in 80-90% of patients.

Noise effects on inner ear

Noise effects on inner ear (ICD-10 H83.3; ICD-11 AB37): inner ear damage, chiefly cochlear hair-cell loss, from acute acoustic trauma or chronic noise exposure; includes noise-induced hearing loss, 3-6 kHz notching, tinnitus, and vestibular effects.

Non paralytic strabismus

Non paralytic strabismus (ICD-11 9C80; concomitant strabismus) is eye deviation with full ocular movements in each eye, comitant in all gaze directions, comprising 75–95% of strabismus cases, treated with refractive correction, botulinum toxin, or surgery.

Non-24 hour sleep-wake rhythm disorder

Non-24-hour sleep-wake syndrome (N24SWD), or free-running disorder, is a circadian rhythm sleep-wake disorder in which the clock fails to entrain to the 24-hour day, affecting 50-70% of totally blind people and causing daily sleep drift, cyclical insomnia, and daytime sleepiness.

Non-convulsive status epilepticus

Non-convulsive status epilepticus (NCSE, ICD-11 8A66.1) is prolonged seizure activity without convulsions, diagnosed by EEG. Altered mental status is the hallmark; outcome depends on etiology, worst after anoxic injury.

Non-restorative sleep

Non-restorative sleep, also called unrefreshing sleep or waking up tired, is sleep felt to be unrefreshing despite adequate duration. Dropped from ICSD-3 insomnia criteria; linked to sleep apnea, fibromyalgia, and chronic fatigue syndrome.

Non-specific autoimmune cerebellar ataxia without characteristic antibodies

Non-specific autoimmune cerebellar ataxia without characteristic antibodies, or primary autoimmune cerebellar ataxia (PACA), is suspected immune-mediated cerebellar ataxia with no known trigger or pathogenic antibody; diagnosed by 2020 task force criteria using clinical, MRI/MRS, and CSF findings.

Non-terminal myelocystocele

Non-terminal myelocystocele (ORPHA:645340), a rare closed spinal dysraphism above the conus with a skin-covered CSF sac; abortive and complete subtypes; favorable prognosis versus myelomeningocele.

Noninfectious intermediate uveitis

Noninfectious intermediate uveitis, also called pars planitis when idiopathic, is chronic inflammation of the vitreous, pars plana, and peripheral retina; treated with corticosteroids, immunosuppressants, and adalimumab.

Nonorganic visual loss

Nonorganic visual loss, also called functional visual loss, is reduced visual acuity or field with no organic lesion found, accounting for about 12% of neuro-ophthalmology diagnoses.

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.

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.

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.

Occipital neuralgia

Occipital neuralgia, also called Arnold's neuralgia or C2 neuralgia, is paroxysmal stabbing pain in the greater, lesser, or third occipital nerve distributions, first described in 1821, incidence 3.2 per 100,000, confirmed by diagnostic nerve block.

Occult macular dystrophy

Occult macular dystrophy (OMD, Miyake disease, 三宅病) is a rare autosomal dominant retinal disease causing progressive central vision loss with a normal-appearing fundus, normal full-field ERG, attenuated focal macular ERG, and RP1L1 mutations.

Ocular albinism with late-onset sensorineural deafness

Ocular albinism with late-onset sensorineural deafness (OASD), also called ocular albinism with late-onset sensorineural hearing loss, is a rare X-linked disorder with severe vision impairment and moderately severe hearing loss appearing from adolescence to middle age.

Ocular anomalies-axonal neuropathy-developmental delay syndrome

Ocular anomalies-axonal neuropathy-developmental delay syndrome, or Harel-Yoon syndrome (HAYOS), is a rare ATAD3A (1p36.33) mitochondrial neurodevelopmental disorder with hypotonia, spasticity, optic atrophy, neuropathy, and cardiomyopathy; OMIM 617183.