Human health and medicine

Classic heparin-induced thrombocytopenia

Classic heparin-induced thrombocytopenia (cHIT, typical-onset HIT) is a prothrombotic IgG anti-PF4/heparin adverse drug reaction causing platelet falls 5–10 days after heparin, with 50–70% thrombosis risk, diagnosed by 4Ts score plus immunoassay and functional assays and treated with non-heparin anticoagulants.

Classic Hodgkin lymphoma

Classic Hodgkin lymphoma, also written classical Hodgkin's lymphoma, is a cancer of the immune system marked by Hodgkin and Reed-Sternberg cells, accounting for about 95% of Hodgkin lymphoma cases.

Classic mycosis fungoides

Classic mycosis fungoides (Alibert-Bazin type, ORPHA:2584) is the most common form of cutaneous T-cell lymphoma, progressing slowly from patches on sun-protected skin to plaques and tumors, treated stage-adapted with skin-directed therapy first.

Classical cystic fibrosis

Classical (classic, typical) cystic fibrosis, ICD-11 CA25.0, is the severe majority form of CF: CFTR mutations, sweat chloride >60 mmol/l, pancreatic insufficiency, progressive lung disease, distinct from atypical CF.

Classical Ehlers-Danlos syndrome

Classical Ehlers-Danlos syndrome (cEDS), formerly EDS classical type, is a heritable connective tissue disorder with hyperextensible skin, atrophic scarring, and joint hypermobility, caused by COL5A1 or COL5A2 variants affecting type V collagen.

Classical Hodgkin lymphoma, mixed cellularity type

Mixed cellularity classical Hodgkin lymphoma is a subtype making up 20–25% of cases, strongly linked to Epstein–Barr virus, more common in males, and typically presenting at advanced stages.

Classical scabies

Classical scabies, also called common or typical scabies, is the standard form of infestation by Sarcoptes scabiei var. hominis with 10–15 mites, nocturnal itch, burrows in finger webs and wrists, and permethrin treatment, distinct from crusted scabies.

Classical-like Ehlers-Danlos syndrome type 1

Classical-like Ehlers-Danlos syndrome type 1 (TNXB-related clEDS) is an autosomal recessive connective tissue disorder from biallelic TNXB variants causing tenascin-X deficiency, with joint hypermobility, hyperextensible skin, easy bruising, and no atrophic scarring.

Classical-like Ehlers-Danlos syndrome type 2

Classical-like Ehlers-Danlos syndrome type 2, also known as AEBP1-related EDS, is a rare autosomal recessive connective tissue disorder causing joint hypermobility and fragile, stretchy skin.

Classification and diagnosis of acute lymphoblastic leukemia

The classification and diagnosis of acute lymphoblastic leukemia covers the 20% blast threshold, obligatory morphology, flow cytometry, and molecular genetics, and the 2022 WHO and ICC genetic subgroups.

Classification of acute myeloid leukemia

Acute myeloid leukemia is classified by the morphologic FAB system, its eight subtypes M0–M7, and the genetic 2022 WHO and ICC classifications that define disease by mutations.

Classification of mental disorders

Classification of mental disorders: organizing mental, behavioral, and neurodevelopmental conditions into diagnostic categories via ICD-11 (WHO, effective 2022) and DSM-5-TR (APA, 2022), with dimensional alternatives RDoC and HiTOP.

Classification of obesity

Classification of obesity: WHO BMI-based classes (obesity ≥30 kg/m², classes I–III), ICD code 5B81, the 2025 Lancet Commission's clinical vs preclinical obesity diagnosis, and the Edmonton Obesity Staging System (EOSS) complications-based staging.

Classification of personality disorders

Classification of personality disorders: how DSM and ICD categorize personality pathology. DSM-5-TR keeps 10 categorical disorders in three clusters; ICD-11 (2022) uses severity plus five trait domains.

Oct 10, 2026

Claude Beck

Claude Schaeffer Beck (1894–1971) was an American cardiac surgeon in Cleveland who performed the first successful human defibrillation in 1947 and described Beck's triad of cardiac tamponade.

Claudication

Claudication (intermittent claudication) is exertional leg pain relieved by rest, caused by atherosclerotic PAD, affecting about 4.5% of people over 40; treated with supervised exercise, cilostazol, and revascularization when needed.

Claustrophobia

Claustrophobia: persistent irrational fear of enclosed or confined spaces, a situational specific phobia. Also suffocation-restriction two-factor model; affects about 10% of UK people lifetime; treated with CBT and exposure therapy.

Clavicle

Clavicle (collarbone): the doubly curved bone linking sternum and scapula, the only bony connection of arm to trunk. Ossifies first among long bones; fractures are ~5% of adult fractures.

Clavulanic acid

Clavulanic acid, from Streptomyces clavuligerus, is a β-lactam β-lactamase inhibitor with weak antibacterial activity, used with amoxicillin (Augmentin) and ticarcillin (Timentin) against class A β-lactamase producers.

Clazakizumab

Clazakizumab, once codeveloped as BMS-945429, is a humanized monoclonal antibody that blocks interleukin-6; its phase 3 kidney transplant trial failed, and Eli Lilly licensed it in 2026.

Clazosentan

Clazosentan (Pivlaz), a selective endothelin A receptor antagonist by Actelion/Idorsia, approved in Japan (2022) to prevent cerebral vasospasm after aneurysmal subarachnoid hemorrhage surgery; reduces vasospasm but not mortality or functional outcome.

CLCN4-related X-linked intellectual disability syndrome

CLCN4-related X-linked intellectual disability syndrome, also called Raynaud-Claes syndrome (MRXSRC, OMIM 300114), is a rare Xp22.2 chloride/proton exchanger gene disorder causing intellectual disability, epilepsy, and behavioral problems in males and females.

Cleaning

Cleaning: removal of soil, dirt, and germs from surfaces using water, soap, and scrubbing; distinct from sanitizing and disinfecting, which it should precede.

Cleanliness

Cleanliness is freedom from dirt and disease-causing microbes; hygiene is the practices reducing pathogen transmission. Covers handwashing mechanisms, 1.4 million WASH-preventable deaths, JMP hygiene ladders, ritual purity traditions, and 2025 WHO guidelines.

Clear aligners

Clear aligners are removable clear plastic orthodontic trays, including Invisalign, worn about 22 hours daily to treat mild-to-moderate malocclusion; less effective than braces for complex movements.

Clear cell adenocarcinoma of the ovary

Clear cell adenocarcinoma of the ovary (ovarian clear cell carcinoma, OCCC, ORPHA:398971) is a rare epithelial ovarian cancer, ~10% of EOC, linked to endometriosis, ARID1A/PIK3CA mutations, good early-stage prognosis, and platinum-resistant advanced disease.

Clear cell renal carcinoma

Clear cell renal cell carcinoma (ccRCC, conventional renal cell carcinoma) is the most common kidney cancer in adults, 70–80% of RCC, defined by clear lipid- and glycogen-rich cytoplasm and VHL/HIF pathway loss, with worse prognosis than papillary or chromophobe subtypes.