Nervous and sensory conditions

Malignant neoplasm of orbit

Malignant neoplasm of orbit (ICD-11 2D04, ICD-10 C69.6) covers primary, secondary, and metastatic orbital cancers. Lymphoma, mainly MALT B-cell type, predominates in adults; rhabdomyosarcoma in children; incidence is rising.

Malignant peripheral nerve sheath tumor

Malignant peripheral nerve sheath tumor (MPNST), also called malignant schwannoma or neurofibrosarcoma, is a rare aggressive soft tissue sarcoma of nerve sheath cells; about half of cases occur in neurofibromatosis type 1, with five-year survival roughly 20 to 69%.

Manganese excess

Manganese excess (manganism): neurotoxicity from elevated manganese, causing parkinsonism in adults and cognitive-motor deficits in children; basal ganglia accumulation, biliary excretion, occupational welding/mining and water exposures, FNB UL 11 mg/day adults.

Marcus-Gunn syndrome

Marcus-Gunn syndrome, or Marcus Gunn jaw-winking syndrome (MGJWS), is a congenital ptosis with trigemino-oculomotor synkinesis: the drooping upper eyelid elevates during jaw movements, occurring in roughly 2-13% of congenital ptosis cases.

Marinesco-Sjögren syndrome

Marinesco-Sjögren syndrome (MSS), also called Garland-Moorhouse syndrome, is a rare autosomal recessive disorder caused by SIL1 gene variants, marked by cerebellar ataxia, early-onset cataracts, myopathy, and often intellectual disability.

Martin R. Gluck

Martin R. Gluck (1957–2023) was an American neurologist and neuroscientist at the Bronx VA Medical Center and Mount Sinai, known for research on dopamine oxidation and mitochondrial dysfunction in Parkinson's disease.

McLeod syndrome

McLeod neuroacanthocytosis syndrome (MLS, X-linked McLeod syndrome, XK disease): rare X-linked recessive XK-gene disorder with absent Kx antigen, chorea, cardiomyopathy, acanthocytosis; distinct from O'Sullivan–McLeod syndrome.

Measles complicated by encephalitis

Measles complicated by encephalitis: brain inflammation from measles virus infection, about 1 per 1,000 cases, often causing permanent brain damage; includes ADEM, MIBE, and SSPE forms.

Mechanical strabismus

Mechanical (restrictive) strabismus: eye misalignment from physical limitation of extraocular muscle movement, not nerve palsy. Causes include thyroid eye disease, orbital fractures, scarring, and congenital fibrosis; diagnosed with forced duction testing.

Medullary tegmental cap dysplasia

Medullary tegmental cap dysplasia (MTCD, ORPHA:727881) is a rare brainstem malformation, first described by Barkovich in 2005, with an abnormal cap protruding from the posterior medullary surface, variable neurodevelopment, and links to Joubert syndrome and FOP.

Meesmann corneal dystrophy

Meesmann corneal dystrophy (MECD, juvenile epithelial corneal dystrophy, Meesmann-Wilke syndrome) is a rare autosomal dominant corneal epithelial disorder from KRT3 or KRT12 mutations, causing tiny intraepithelial microcysts with little vision loss.

Mega-cisterna magna

Mega-cisterna magna (MCM), enlarged cisterna magna over 10 mm anteroposterior with normal cerebellar vermis and no hydrocephalus; a mild Dandy-Walker complex anomaly, usually asymptomatic and incidental.

Megalencephalic leukoencephalopathy with subcortical cysts

Megalencephalic leukoencephalopathy with subcortical cysts (MLC, Van der Knaap disease) is a rare leukodystrophy with infantile macrocephaly, swollen white matter, anterior temporal cysts, and genes MLC1, GLIALCAM, GPRC5B, AQP4.

Megalencephaly-polymicrogyria-postaxial polydactyly-hydrocephalus syndrome

MPPH syndrome, also called megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome, is a rare autosomal dominant brain overgrowth disorder caused by AKT3, CCND2, or PIK3R2 gain-of-function variants in the PI3K-AKT-mTOR pathway, with polymicrogyria, hydrocephalus, and postaxial polydactyly.

Megalocornea-intellectual disability syndrome

Megalocornea-intellectual disability syndrome, also called MMR or Neuhäuser syndrome (OMIM 249310), is an extremely rare autosomal recessive disorder combining enlarged corneas without glaucoma, hypotonia, intellectual disability, seizures, and facial dysmorphism, with about 40 reported cases and unknown genetic cause.

MEGDEL syndrome

MEGDEL syndrome (MEGDHEL), a rare autosomal recessive SERAC1-related neurometabolic disorder with 3-methylglutaconic aciduria, neonatal hepatopathy, hypotonia, dystonia, spasticity, progressive deafness, and Leigh-like brain changes.

Meibomian gland dysfunction

Meibomian gland dysfunction (MGD), chronic obstruction or secretion abnormality of the eyelid oil glands, is the leading cause of evaporative dry eye; pooled prevalence about 36%, treated with warm compresses, antimicrobials, and thermal pulsation devices.

Melanoma associated retinopathy

Melanoma associated retinopathy (MAR), ICD-11 9B71.40, is a rare paraneoplastic retinopathy of metastatic melanoma caused by TRPM1 autoantibodies against retinal ON-bipolar cells, causing night blindness, photopsias, field loss, and an electronegative ERG.

Melanoma of choroid

Melanoma of choroid (choroidal melanoma, uveal melanoma): malignant melanocyte tumor of the eye's choroid, the most common primary intraocular adult malignancy; treated by plaque brachytherapy or proton radiation, metastasizing mainly to the liver.

Melanoma of ciliary body

Melanoma of ciliary body, a uveal melanoma subtype (~6% of cases), arises behind the iris, is diagnosed late, carries poor prognosis, and is treated with plaque radiotherapy, proton beam, iridocyclectomy, or enucleation.

Meningism

Meningism, also called meningismus, is the syndrome of headache, neck stiffness, and photophobia suggesting meningeal irritation when the meninges are not actually inflamed, so it requires evaluation to find the cause.

Meningitis

Meningitis is inflammation of the meninges, the lining of the brain and spinal cord, caused by bacteria, viruses, fungi, or parasites. Bacterial meningitis kills about 1 in 6 affected; the African meningitis belt bears the highest burden.

Meningitis due to Cryptococcus neoformans

Meningitis due to Cryptococcus neoformans (cryptococcal meningitis): fungal CNS infection from inhaled C. neoformans, mainly in advanced HIV; diagnosed by CrAg and culture; treated with liposomal amphotericin B, flucytosine, fluconazole.

Meningitis due to Haemophilus influenzae

Meningitis due to Haemophilus influenzae (ICD-11 1D01.00), historically mainly Hib serotype b, was the leading cause of childhood bacterial meningitis before conjugate vaccines cut US cases by over 99%.

Meningitis due to mumps virus

Meningitis due to mumps virus is an aseptic meningitis caused when the mumps virus spreads to the membranes around the brain, occurring in up to 10% of unvaccinated mumps cases.

Meningococcal disease

Meningococcal disease, invasive infection by Neisseria meningitidis (meningococcus), causes bacterial meningitis and septicemia; six serogroups (A, B, C, W, X, Y) drive disease, with 10-15% case fatality and MenACWY/MenB vaccines for prevention.

Meningoencephalitis

Meningoencephalitis is simultaneous inflammation of the meninges and brain parenchyma, usually from viral, bacterial, or fungal infection. ICU mortality runs 11–25%; early acyclovir and cephalosporins improve outcomes; Naegleria fowleri causes a rare, nearly always fatal amebic form.

Mercury poisoning

Mercury poisoning, also called mercurialism or Minamata disease in its outbreak form, is toxicity from elemental, inorganic, or organic mercury, chiefly methylmercury in fish and mercury vapor at work, damaging the nervous system and kidneys.

Mesial temporal lobe epilepsy with hippocampal sclerosis

Epilepsy with mesial temporal sclerosis (ICD-11 8A60.7), also called epilepsy with hippocampal or Ammon's horn sclerosis: focal epilepsy from hippocampal scarring, often after childhood febrile seizures, frequently drug-resistant but highly surgically treatable.