Nervous and sensory conditions

Lesion of femoral nerve

Lesion of femoral nerve (femoral neuropathy, ICD-11 8C11.2): damage to the L2–L4 femoral nerve causing weak knee extension and hip flexion. Main causes are compression and perioperative stretch; recovery is common but often incomplete.

Lesion of sciatic nerve

Lesion of sciatic nerve (ICD-11 8C11.0): disease or damage to the sciatic nerve trunk (L4-S3), causing sciatica, foot drop, and sensory loss; causes include trauma, compression, hip surgery, and piriformis syndrome.

Lethal ataxia with deafness and optic atrophy

Lethal ataxia with deafness and optic atrophy, or Arts syndrome (OMIM 301835), is an extremely rare X-linked recessive PRPS1 loss-of-function disorder causing congenital deafness, ataxia, hypotonia, intellectual disability, and optic atrophy, usually fatal before age 5.

Leukodystrophy

Leukodystrophy: a group of over 50 rare inherited genetic disorders damaging CNS white matter myelin (also called the leukodystrophies). Progressive; diagnosed by MRI and genetic testing; treated with transplant or, for early MLD, Lenmeldy gene therapy.

Leukoencephalopathy with bilateral anterior temporal lobe cysts

Leukoencephalopathy with bilateral anterior temporal lobe cysts (ORPHA:139444) is a rare nonprogressive neurological disorder of infancy with intellectual deficit, spasticity, motor retardation, temporal lobe cysts on MRI, sensorineural deafness, and unknown, possibly autosomal recessive cause.

Leukoencephalopathy with brain stem and spinal cord involvement-high lactate syndrome

LBSL, leukoencephalopathy with brain stem and spinal cord involvement-high lactate syndrome (MIM 611105), is a rare autosomal recessive leukodystrophy caused by DARS2 variants, marked by selective tract MRI abnormalities, elevated white matter lactate, and progressive ataxia and spasticity.

Leukoencephalopathy with calcifications and cysts

Leukoencephalopathy with calcifications and cysts (LCC, Labrune syndrome) is a rare autosomal recessive SNORD118-related cerebral microangiopathy with the MRI triad of white matter disease, calcifications, and cysts, purely neurological and distinct from Coats plus.

Leukoencephalopathy-spondyloepimetaphyseal dysplasia syndrome

Leukoencephalopathy-spondyloepimetaphyseal dysplasia syndrome (H-SMD, ORPHA:83629, OMIM 300232) is a rare X-linked recessive AIFM1-related disorder combining hypomyelinating leukodystrophy with spondylometaphyseal dysplasia, onset in infancy.

Leukoencephalopathy-thalamus and brainstem anomalies-high lactate syndrome

LTBL (leukoencephalopathy with thalamus and brainstem involvement and high lactate) is a rare EARS2-related mitochondrial myelination disorder with infantile onset, MRI thalamus/brainstem lesions, high lactate, and mild or severe phenotypes.

Lhermitte's sign

Lhermitte's sign, also called Lhermitte's phenomenon or the barber chair phenomenon, is an electric shock-like sensation down the spine triggered by neck flexion, best known as a symptom of multiple sclerosis.

Limbal stem cell deficiency

Limbal stem cell deficiency (LSCD), a rare corneal disorder (1-5/10,000) from loss or dysfunction of limbal stem cells, causing corneal conjunctivalization, neovascularization, and vision loss; treated with limbal transplants such as CLAU, SLET, and CLET.

Lisch epithelial corneal dystrophy

Lisch epithelial corneal dystrophy, also called band-shaped and whorled microcystic dystrophy, is a rare corneal dystrophy with feathery gray opacities that first appear in childhood and slowly progress.

Lissencephaly due to LIS1 mutation

Lissencephaly due to LIS1 mutation, also called PAFAH1B1-related lissencephaly, is a rare autosomal dominant cortical malformation on 17p13.3 causing posterior smooth brain, severe epilepsy evolving from West to Lennox-Gastaut syndrome, and developmental delay.

List of NFL players with chronic traumatic encephalopathy

NFL players diagnosed with chronic traumatic encephalopathy (CTE), a tau protein brain disease from repeated head impacts, confirmed only posthumously; includes Mike Webster, Dave Duerson, Junior Seau, John Mackey, Ken Stabler, Aaron Hernandez, and Marshawn Kneeland, with prevalence studies from Boston University's brain bank.

Lithium toxicity

Lithium toxicity (lithium poisoning, overdose) is harmful accumulation of the bipolar disorder drug lithium, in acute, chronic, or acute-on-chronic patterns; treated with IV fluids and hemodialysis per EXTRIP criteria, with SILENT as permanent neurologic risk.

Lobar haemorrhage

Lobar haemorrhage (ICD-11 8B00.1), also called superficial or cortical intracerebral haemorrhage, is bleeding within the cerebral lobes. Main causes are cerebral amyloid angiopathy, hypertension, anticoagulation, malformations, and tumors; larger but better prognosis than deep ICH.

Logopenic progressive aphasia

Logopenic progressive aphasia (LPA, lvPPA) is a variant of primary progressive aphasia marked by word-finding difficulty and impaired sentence repetition with spared single-word comprehension, usually linked to Alzheimer disease and left temporoparietal atrophy.

Logorrhea (psychology)

Logorrhea (logorrhoea) is excessive, uncontrollable speech flow, a clinical sign in mania, schizophrenia, catatonia, Wernicke's aphasia, and dementia; from Greek logos plus rhein, coined from diarrhea, first recorded 1878.

Lorenzo's Oil

Lorenzo's oil is a 4:1 oleic-erucic acid dietary mixture developed by the Odone family for adrenoleukodystrophy; it normalizes VLCFA levels, may help asymptomatic boys, and inspired the 1992 film.

Lujan-Fryns syndrome

Lujan-Fryns syndrome (Lujan syndrome, X-linked intellectual disability with marfanoid habitus, OMIM 309520): rare X-linked recessive MED12-related disorder in males with mild-to-moderate intellectual disability, marfanoid tall stature, distinct facial dysmorphism, hypernasal speech, and psychiatric problems.

Lumbar spinal stenosis

Lumbar spinal stenosis (LSS), degenerative narrowing of the lumbar spinal canal causing neurogenic claudication in older adults; diagnosed by symptoms plus MRI, treated conservatively or by decompression, with fusion and spacers showing no added benefit.

Lumbosacral radiculoplexopathy

Lumbosacral radiculoplexopathy, including diabetic lumbosacral radiculoplexus neuropathy (diabetic amyotrophy, Bruns-Garland syndrome), is a painful, asymmetric proximal lower-limb neuropathy from microvasculitic ischemic nerve injury, with no proven immunotherapy.

Lyme neuroborreliosis

Lyme neuroborreliosis (LNB) is nervous system infection with Borrelia burgdorferi sensu lato, affecting 3–15% of European Lyme cases; diagnosis requires CSF pleocytosis and intrathecal antibody index, treated with 14 days of antibiotics.

Macrocephaly

Macrocephaly, also called megalencephaly-related head enlargement, is an occipitofrontal head circumference over 2 SD above the age and sex mean, affecting up to 5% of children, with causes ranging from benign familial macrocephaly and BESS to over 200 genetic disorders and hydrocephalus.

Macrocephaly-intellectual disability-neurodevelopmental disorder-small thorax syndrome

Macrocephaly-intellectual disability-neurodevelopmental disorder-small thorax syndrome, also called MINDS or Smith-Kingsmore syndrome, is a rare autosomal dominant MTOR gain-of-function disorder with macrocephaly, intellectual disability, seizures, and small thorax.

Macular corneal dystrophy

Macular corneal dystrophy is a rare autosomal recessive corneal disease caused by CHST6 gene mutations, in which glycosaminoglycan buildup clouds both corneas and progressively impairs vision.

Macular degeneration

Macular degeneration (AMD), also called age-related macular degeneration, is a retinal disease blurring central vision. Dry and wet types; drusen hallmark; treated with anti-VEGF injections, AREDS supplements, and GA drugs pegcetacoplan and avacincaptad pegol.

Macular telangiectasia

Macular telangiectasia (MacTel), chiefly type 2 or perifoveal telangiectasia, is a rare bilateral retinal disease combining telangiectatic capillaries with photoreceptor and Müller cell degeneration, linked to serine and deoxysphingolipid metabolism, with Encelto approved in 2025.

Malignant neoplasm of choroid

Malignant neoplasm of choroid (ICD-11 2D05): primary choroidal melanoma or, more commonly in adults, choroidal metastasis from breast or lung cancer; treated mainly with radiotherapy and systemic therapy.