Clinical Glossary

47 key terms — definitions, clinical pearls, and USMLE connections

Addison's Disease

Endocrinology

Primary adrenal insufficiency due to destruction of the adrenal cortex, leading to deficiency of cortisol and aldosterone.

Clinical Pearl

Hyperpigmentation (due to elevated ACTH/MSH) distinguishes primary from secondary adrenal insufficiency.

Angle-Closure Glaucoma

Sensory Organs

Acute glaucoma from physical obstruction of the trabecular meshwork by the peripheral iris, causing sudden IOP elevation and optic nerve damage.

Clinical Pearl

Ophthalmological emergency. Presents with severe eye pain, nausea, halos, mid-dilated fixed pupil. Can be precipitated by anticholinergic drugs. Treat with IV acetazolamide + laser iridotomy.

Anion Gap

Nephrology

The difference between measured cations (Na+) and anions (Cl- + HCO3-). Normal = 8–12 mEq/L.

Clinical Pearl

Elevated anion gap metabolic acidosis: MUDPILES — Methanol, Uremia, DKA, Propylene glycol, Isoniazid, Lactic acidosis, Ethylene glycol, Salicylates.

Anti-CCP

Allergy/Rheum

Anti-citrullinated protein antibodies; highly specific for Rheumatoid Arthritis.

Clinical Pearl

Anti-CCP can appear years before clinical RA and predicts a more erosive disease course.

Apoptosis

Path Anatomy

Programmed cell death characterized by cell shrinkage, chromatin condensation, and formation of apoptotic bodies, without inflammation.

Clinical Pearl

Apoptosis is mediated by caspases and is physiological. It differs from necrosis, which is always pathological and triggers inflammation.

ARDS

Pulmonology

Acute Respiratory Distress Syndrome; diffuse alveolar damage, non-cardiogenic pulmonary edema, and refractory hypoxemia.

Clinical Pearl

Defined by PaO2/FiO2 ratio < 300. Berlin definition: mild (200–300), moderate (100–200), severe (< 100).

Ascites

Gastroenterology

Accumulation of fluid in the peritoneal cavity.

Clinical Pearl

SAAG ≥ 1.1 g/dL confirms portal hypertension. SAAG < 1.1 g/dL suggests other causes (malignancy, TB peritonitis).

Atrial Fibrillation

Cardiology

Irregular, chaotic atrial rhythm with absence of distinct P waves on ECG.

Clinical Pearl

CHA2DS2-VASc score determines anticoagulation need to prevent thromboembolic stroke.

Barrett's Esophagus

Gastroenterology

Metaplastic replacement of squamous esophageal epithelium with specialized intestinal columnar epithelium, a complication of chronic GERD.

Clinical Pearl

Barrett's increases the risk of esophageal adenocarcinoma by 30–40 fold. Regular surveillance endoscopy is required.

Beck's Triad

Cardiology

Classic triad of cardiac tamponade: hypotension, distended neck veins (JVD), and muffled heart sounds.

Clinical Pearl

Pulsus paradoxus (> 10 mmHg drop in systolic BP during inspiration) is a key additional finding in cardiac tamponade.

BPPV

Sensory Organs

Benign Paroxysmal Positional Vertigo; most common cause of vertigo, caused by displaced otoliths (canalith) in the semicircular canals.

Clinical Pearl

Dix-Hallpike test is diagnostic (brief rotatory nystagmus). Treatment: Epley maneuver (canalith repositioning). Resolves spontaneously in most cases.

Cirrhosis

Gastroenterology

Irreversible diffuse hepatic fibrosis with regenerative nodule formation, representing the end stage of chronic liver disease.

Clinical Pearl

Child-Pugh score and MELD score assess severity and predict prognosis. Ascites marks the transition from compensated to decompensated cirrhosis.

Cup-to-Disc Ratio

Sensory Organs

Ratio of the optic cup diameter to the optic disc diameter. Normal < 0.5. Increased ratio (> 0.6) suggests glaucomatous optic nerve damage.

Clinical Pearl

Asymmetry in cup-to-disc ratio between eyes is more suspicious for glaucoma than a symmetrically increased ratio.

Cushing's Syndrome

Endocrinology

Clinical syndrome from prolonged exposure to excess glucocorticoids, presenting with central obesity, moon facies, buffalo hump, purple striae, and hypertension.

Clinical Pearl

Most common cause is iatrogenic. Most common endogenous cause is pituitary ACTH-secreting adenoma (Cushing's disease).

Dawson's Fingers

Neurology

Periventricular demyelinating plaques in Multiple Sclerosis oriented perpendicular to the lateral ventricles, appearing finger-like on sagittal MRI.

Clinical Pearl

Best seen on sagittal FLAIR MRI. The orientation is due to plaques forming along medullary veins. Part of McDonald criteria for MS diagnosis.

Diabetic Retinopathy

Sensory Organs

Microvascular complication of diabetes affecting the retina. NPDR (non-proliferative): microaneurysms, dot-blot hemorrhages, hard exudates. PDR (proliferative): neovascularization.

Clinical Pearl

Neovascularization in PDR can cause vitreous hemorrhage and tractional retinal detachment. Treat with pan-retinal photocoagulation or anti-VEGF injections.

DKA

Endocrinology

Diabetic Ketoacidosis; hyperglycemia (> 250 mg/dL), metabolic acidosis (pH < 7.3), and ketonemia. Primarily Type 1 DM.

Clinical Pearl

Precipitating factors: infection, missed insulin doses, MI. Despite total body K+ depletion, serum K+ may be normal or elevated initially due to acidosis.

Endolymphatic Hydrops

Sensory Organs

Abnormal accumulation of endolymph in the membranous labyrinth of the inner ear; the underlying pathophysiology of Ménière's Disease.

Clinical Pearl

Leads to distension and eventual rupture of the membranous labyrinth, mixing endo- and perilymph, disrupting hair cell function and causing episodic vertigo.

FENa

Nephrology

Fractional Excretion of Sodium. Formula: (urine Na × plasma Cr) / (plasma Na × urine Cr) × 100.

Clinical Pearl

FENa < 1% = prerenal AKI. FENa > 2% = intrinsic AKI. Unreliable with diuretics — use FEUrea instead.

Graves' Disease

Endocrinology

Autoimmune hyperthyroidism caused by TSH receptor-stimulating antibodies (TRAb), leading to diffuse goiter, exophthalmos, and pretibial myxedema.

Clinical Pearl

Exophthalmos is caused by glycosaminoglycan deposition in the retro-orbital space and does NOT resolve with treatment of hyperthyroidism.

Guillain-Barré Syndrome

Neurology

Acute autoimmune demyelinating polyradiculoneuropathy presenting with ascending flaccid paralysis, areflexia, and albuminocytologic dissociation in CSF.

Clinical Pearl

Most commonly triggered by Campylobacter jejuni infection. Albuminocytologic dissociation = elevated CSF protein with normal cell count. Treatment: IVIG or plasmapheresis.

HHS

Endocrinology

Hyperosmolar Hyperglycemic State; severe hyperglycemia (> 600 mg/dL) and hyperosmolarity (> 320 mOsm/kg) without significant ketoacidosis. Type 2 DM.

Clinical Pearl

HHS has higher mortality than DKA. Profound dehydration can cause neurological manifestations including seizures and coma.

Hypersensitivity

Allergy/Rheum

Exaggerated immune response to an antigen. Type I (IgE-mediated), Type II (antibody-mediated), Type III (immune complex), Type IV (T-cell mediated).

Clinical Pearl

Mnemonic ACID: Anaphylactic (I), Cytotoxic (II), Immune complex (III), Delayed/T-cell (IV).

Internuclear Ophthalmoplegia

Neurology

Impaired adduction of the ipsilateral eye with nystagmus of the contralateral abducting eye, caused by a lesion in the medial longitudinal fasciculus (MLF).

Clinical Pearl

Bilateral INO in a young patient is virtually pathognomonic for Multiple Sclerosis. Unilateral INO in an elderly patient suggests brainstem stroke.

Ischemic Penumbra

Neurology

Zone of brain tissue surrounding the ischemic core that is functionally impaired but structurally viable; the therapeutic target in acute ischemic stroke.

Clinical Pearl

The penumbra can be salvaged by rapid reperfusion (tPA within 4.5h or thrombectomy within 24h). Time is brain: 1.9 million neurons lost per minute.

Lewy Body

Neurology

Intracytoplasmic eosinophilic inclusion composed of aggregated alpha-synuclein protein; the pathological hallmark of Parkinson's Disease and Lewy Body Dementia.

Clinical Pearl

Alpha-synuclein aggregation is also seen in Multiple System Atrophy. REM sleep behavior disorder may precede motor symptoms of Parkinson's by years.

Malar Rash

Allergy/Rheum

Butterfly erythematous rash across the cheeks and nasal bridge, sparing the nasolabial folds; classic feature of SLE.

Clinical Pearl

Malar rash spares the nasolabial folds, distinguishing it from rosacea which involves them.

Ménière's Disease

Sensory Organs

Inner ear disorder characterized by the triad of episodic vertigo (20 min–12h), fluctuating low-frequency sensorineural hearing loss, and tinnitus with aural fullness.

Clinical Pearl

Distinguished from BPPV by duration (minutes to hours vs. seconds) and associated hearing loss/tinnitus. Low-sodium diet and diuretics reduce endolymph volume.

Minimal Change Disease

Nephrology

Most common cause of nephrotic syndrome in children; normal light microscopy, effacement of podocyte foot processes on EM.

Clinical Pearl

Associated with Hodgkin's lymphoma in adults. Highly responsive to corticosteroid therapy.

Myasthenia Gravis

Neurology

Autoimmune neuromuscular junction disorder caused by antibodies against nicotinic acetylcholine receptors (AChR), leading to fatigable muscle weakness.

Clinical Pearl

Ptosis and diplopia are the most common initial symptoms. Weakness worsens with repetitive use and improves with rest. Associated with thymoma in 15% of cases.

Otosclerosis

Sensory Organs

Abnormal bone remodeling that fixates the stapes footplate in the oval window, causing progressive conductive hearing loss in young adults.

Clinical Pearl

Rinne test: negative (BC > AC). Weber lateralizes to affected ear. Paracusis Willisii (hearing better in noisy environments) is characteristic. Treatment: stapedectomy.

Pannus

Allergy/Rheum

Abnormal proliferative granulation tissue from the synovium in RA, which invades and destroys articular cartilage and bone.

Clinical Pearl

Pannus formation is driven by TNF-alpha and IL-6 — explaining the therapeutic targets of biologic DMARDs.

Portal Hypertension

Gastroenterology

Elevated pressure in the portal venous system (> 5 mmHg), most commonly caused by cirrhosis.

Clinical Pearl

Complications: esophageal varices, ascites, splenomegaly, caput medusae. Esophageal varices are the most dangerous — risk of life-threatening hemorrhage.

Presbycusis

Sensory Organs

Age-related sensorineural hearing loss affecting high frequencies first, due to progressive loss of cochlear hair cells and stria vascularis atrophy.

Clinical Pearl

Most common cause of hearing loss in the elderly. Bilateral, symmetric, high-frequency loss. Audiogram shows sloping pattern. Treated with hearing aids.

Retinal Artery Occlusion

Sensory Organs

Sudden, painless, monocular vision loss from occlusion of the central or branch retinal artery; fundoscopy shows pale retina with cherry-red spot at the fovea.

Clinical Pearl

Cherry-red spot occurs because the fovea receives its blood supply directly from the choroid, remaining perfused while the surrounding ischemic retina turns pale.

Rinne Test

Sensory Organs

Tuning fork test comparing air conduction (AC) to bone conduction (BC). Normal: AC > BC (Rinne positive). Conductive loss: BC > AC (Rinne negative). SNHL: AC > BC but both reduced.

Clinical Pearl

A false-negative Rinne can occur in severe unilateral SNHL — bone conduction is heard by the contralateral cochlea. Weber test helps clarify.

SIADH

Endocrinology

Syndrome of Inappropriate ADH secretion; hyponatremia, low serum osmolality, inappropriately elevated urine osmolality.

Clinical Pearl

Common causes: SCLC (ectopic ADH), CNS disorders, SSRIs, carbamazepine. Treatment is fluid restriction.

SLE Criteria

Allergy/Rheum

Systemic Lupus Erythematosus diagnostic criteria: SOAP BRAIN MD — Serositis, Oral ulcers, Arthritis, Photosensitivity, Blood disorders, Renal disease, ANA, Immunologic markers, Neurological disorders, Malar rash, Discoid rash.

Clinical Pearl

Anti-dsDNA antibodies correlate with disease activity and are particularly associated with lupus nephritis.

Subarachnoid Hemorrhage

Neurology

Bleeding into the subarachnoid space, most commonly from rupture of a saccular (berry) aneurysm at arterial bifurcations in the Circle of Willis.

Clinical Pearl

Classic presentation: 'thunderclap headache' — worst headache of life, sudden onset. CT head is 98% sensitive within 12h. If CT negative, lumbar puncture shows xanthochromia.

T-score

Orthopaedics

Bone mineral density compared to a young adult reference population. T-score ≤ -2.5 = osteoporosis; -1.0 to -2.5 = osteopenia.

Clinical Pearl

Z-score compares BMD to age-matched controls. Z-score ≤ -2.0 in premenopausal women or men < 50 suggests secondary causes.

Todd's Paralysis

Neurology

Transient focal neurological deficit (typically hemiparesis) following a focal seizure, lasting minutes to hours.

Clinical Pearl

Todd's paralysis can mimic stroke. Key distinction: it follows a witnessed seizure and resolves spontaneously. Imaging is normal.

TRAP (Parkinson's)

Neurology

Mnemonic for the cardinal motor features of Parkinson's Disease: Tremor (resting, pill-rolling), Rigidity (cogwheel), Akinesia/Bradykinesia, Postural instability.

Clinical Pearl

Resting tremor improves with voluntary movement, distinguishing it from essential tremor (which worsens with action). Postural instability is the most disabling feature.

Troponin

Cardiology

Cardiac biomarkers (Troponin I and T) released from damaged myocardial cells. Rise within 3–4 hours, peak at 24–48 hours, remain elevated 7–10 days.

Clinical Pearl

High-sensitivity troponin assays can detect MI within 1–2 hours of symptom onset, enabling rapid rule-in/rule-out protocols.

Uhthoff's Phenomenon

Neurology

Worsening of neurological symptoms in Multiple Sclerosis with increased body temperature (heat, exercise, fever).

Clinical Pearl

Pathognomonic for MS. Occurs because elevated temperature further impairs saltatory conduction in already demyelinated axons. Symptoms resolve when temperature normalizes.

Virchow's Triad

Pulmonology

Three factors predisposing to venous thrombosis: hypercoagulability, venous stasis, and endothelial injury.

Clinical Pearl

Explains increased DVT/PE risk in immobilized patients (stasis), cancer patients (hypercoagulability), and those with venous insufficiency.

Weber Test

Sensory Organs

Tuning fork placed on the vertex; sound lateralizes to the affected ear in conductive hearing loss, and to the unaffected ear in sensorineural hearing loss.

Clinical Pearl

Mnemonic: in CHL, sound goes TO the bad ear (less ambient noise masking); in SNHL, sound goes AWAY from the bad ear (better cochlear function on the good side).

Wernicke's Encephalopathy

Neurology

Acute neurological emergency from thiamine (B1) deficiency presenting with the classic triad: confusion, ophthalmoplegia, and ataxia.

Clinical Pearl

Classic triad is present in only 10% of cases. Treat empirically with IV thiamine BEFORE glucose administration (glucose without thiamine can precipitate Wernicke's in deficient patients).