1,527 articles
Hereditary sensory and autonomic neuropathy type 8
HSAN8 (HSAN type VIII, PRDM12-related congenital insensitivity to pain, OMIM 616488) is an autosomal recessive, neonatal-onset disorder causing congenital pain and temperature insensitivity, corneal scarring, reduced sweating, and self-mutilating injuries with preserved touch and intellect.
Hereditary sensory neuropathy-deafness-dementia syndrome
Hereditary sensory neuropathy-deafness-dementia syndrome (HSAN1E, OMIM 614116) is a rare autosomal dominant DNMT1 mutation disorder causing sensorineural hearing loss, sensory neuropathy, and dementia from adolescence or adulthood, fatal in the fifth to sixth decade.
Herpes simplex meningitis
Herpes simplex meningitis, HSV-2 meningitis, Mollaret's recurrent lymphocytic meningitis: meningeal inflammation from HSV-1/2, mostly HSV-2 after genital herpes; self-limiting, diagnosed by CSF PCR, treated with IV acyclovir.
Herpes simplex virus encephalitis
Herpes simplex virus encephalitis (HSE, HSVE): rare HSV-1 brain infection of frontal and temporal lobes, diagnosed by CSF PCR, treated with IV acyclovir for 14–21 days; 70% mortality untreated, epilepsy and disability common in survivors.
Heterochromia iridum
Heterochromia iridum, also called heterochromia iridis, is a difference in iris color between the two eyes or within one iris. Usually a harmless genetic trait, it can signal Horner syndrome, Waardenburg syndrome, neuroblastoma, injury, or latanoprost use.
Heterophoria
Heterophoria (phoria, latent strabismus), ICD-10 H50.5, is a latent eye misalignment visible only when fusion is broken; about 80% of people have some degree, symptomatic only when vergence compensation fails.
High pressure primary open-angle glaucoma
High pressure primary open-angle glaucoma (high-tension glaucoma, ICD-11 9C61.02): POAG with IOP above 21 mmHg, open angle, reduced trabecular outflow, lamina cribrosa damage, and IOP-lowering treatment goals of 20-30% reduction.
High-functioning autism
High-functioning autism is an informal, non-diagnostic label for autistic people with average or above IQ and speech, roughly DSM-5 level 1 ASD; clinicians and advocates now prefer support-needs language.
History of polio
History of polio: from ancient descriptions and 19th-century epidemics to Salk's 1955 IPV, Sabin's oral vaccine, the 1955 Cutter Incident, and the GPEI's post-1988 campaign that cut cases over 99%, leaving wild polio only in Pakistan and Afghanistan.
Holmes-Adie syndrome
Holmes-Adie syndrome, also called Adie syndrome or tonic pupil-tendon areflexia syndrome, is a benign disorder of ciliary ganglion denervation causing a tonic pupil with light-near dissociation plus absent tendon reflexes, described by Adie and Holmes in 1931.
Homonymous hemianopsia
Homonymous hemianopsia (homonymous hemianopia): loss of the same half of the visual field in both eyes from retrochiasmal lesions (optic tract, LGN, radiations, occipital cortex), usually stroke; macular sparing localizes to occipital cortex.
Hordeolum internum
Hordeolum internum (internal hordeolum, internal stye): acute bacterial infection, usually Staphylococcus aureus, of a meibomian gland inside the eyelid; deeper and more diffuse than an external stye, treated with warm compresses, resolving in 1–2 weeks.
Horizontal conjugate gaze deviation
Horizontal conjugate gaze deviation: both eyes tonically deviated in the same horizontal direction; radiographic form (Rad h-CGD) localizes stroke, seizure, brainstem, and vestibular causes; ICD-11 9C83.10.
Horizontal gaze palsy
Horizontal gaze palsy: inability to move both eyes conjugately in a horizontal direction, usually from a pontine lesion of the PPRF or abducens nucleus (stroke, MS, hemorrhage); congenital form is HGPPS from ROBO3 mutations; ICD-11 9C83.00.
Huntington disease-like 1
Huntington disease-like 1 (HDL1), also called Huntington-like neurodegenerative disorder 1, is a rare autosomal dominant familial prion disease from PRNP octapeptide repeat insertions, mimicking Huntington disease with chorea, dementia, seizures, onset 20-45 years, survival 1-10 years.
Huntington disease-like 2
Huntington disease-like 2 (HDL2) is a rare neurodegenerative disorder mimicking Huntington disease, caused by a JPH3 gene repeat expansion and seen only in people of African ancestry.
Hydranencephaly
Hydranencephaly is a rare congenital malformation in which the cerebral hemispheres are absent and replaced by a cerebrospinal fluid-filled sac, usually caused by blocked carotid arteries in the womb.
Hydrocephalus
Hydrocephalus, "water on the brain," is abnormal CSF build-up in the brain's ventricles. Treated by shunt surgery or endoscopic third ventriculostomy (ETV), often with CPC; congenital, acquired, and NPH types.
Hydrostatic shock
Hydrostatic shock, also called hydraulic shock, is the contested hypothesis that a bullet's ballistic pressure wave injures tissue remote from the wound track; critics attribute remote damage to temporary cavitation instead.
Hyperaesthesia
Hyperaesthesia, also spelled hyperesthesia, is increased sensitivity to stimulation excluding the special senses (ICD-11 MB40.5), a symptom of peripheral and central sensitization commonly accompanying neuropathic pain, caused by nerve injury, metabolic, infectious, autoimmune, or toxic conditions.
Hyperalgesia
Hyperalgesia is increased pain from a stimulus that normally provokes pain, an IASP-defined clinical sign of peripheral or central sensitization; distinguished from allodynia, assessed by quantitative sensory testing, and seen after injury, neuropathy, and opioid use.
Hyperlacrimation
Hyperlacrimation (ICD-11 9A10.3) is overflow of tears from excessive lacrimal gland secretion, caused by drugs, emotion, or trigeminal reflex irritation; distinct from epiphora, a drainage failure.
Hypermetropia
Hypermetropia, also called hyperopia or farsightedness, is a refractive error in which light focuses behind the retina with accommodation relaxed, blurring near vision; caused by short axial length or flat cornea, corrected with plus lenses.
Hyperosmia
Hyperosmia is a quantitatively increased sense of smell, defined as an exceptionally high psychophysical olfactory test score (above the 90th percentile); distinct from olfactory intolerance, and often contradicted by objective testing showing hyposmia.
Hypersomnia
Hypersomnia (hypersomnolence) is excessive daytime sleepiness despite adequate sleep. Includes primary forms (idiopathic hypersomnia, narcolepsy, Kleine-Levin syndrome) and secondary causes; diagnosed by PSG and MSLT after excluding other causes.
Hypertrophic olivary degeneration
Hypertrophic olivary degeneration (HOD), trans-synaptic degeneration of the inferior olivary nucleus after lesions of the Guillain-Mollaret triangle; T2-hyperintense olive hypertrophy on MRI, palatal tremor, no enhancement or diffusion restriction.
Hypnic headache
Hypnic headache, or "alarm clock" headache, is a rare primary headache disorder first described by Raskin in 1988: sleep-only attacks waking patients, lasting 15 minutes to 4 hours, treated with lithium, caffeine, melatonin, or indomethacin.
Hypnopompic hallucinations
Hypnopompic hallucinations are vivid, often visual, dream-like hallucinations that occur on waking from sleep. They are common, and frequent episodes, especially with sleep paralysis, can point to narcolepsy.
Hypomyelination of early myelinating structures
Hypomyelination of early myelinating structures (HEMS) is a rare X-linked genetic disorder in which early-myelinating brain regions stay poorly myelinated, presenting in infancy with nystagmus and ataxia.
Hypomyelination with atrophy of basal ganglia and cerebellum
H-ABC (hypomyelination with atrophy of basal ganglia and cerebellum) is a rare TUBB4A- or UFM1-related leukodystrophy with hypomyelination, putamen and cerebellar atrophy, dystonia, spasticity, and ataxia, onset in infancy.