Clinical anatomy, physiology and methods of larynx research. Acute diseases of the larynx. Laryngeal edema. Laryngeal stenosis. Diphtheria of the larynx. Explain in detail better

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You are a medical research assistant. Research the following topics from the medical textbook library and return a comprehensive, detailed synthesis: 1. Clinical anatomy of the larynx 2. Physiology of the larynx 3. Methods of larynx examination/research 4. Acute diseases of the larynx (acute laryngitis, epiglottitis, etc.) 5. Laryngeal edema (angioedema, allergic edema) 6. Laryngeal stenosis (acute and chronic) 7. Diphtheria of the larynx (croup) Follow this process: - First, search headings_fts for relevant sections using terms like 'larynx', 'laryngeal', 'diphtheria larynx', 'laryngeal stenosis', 'laryngeal edema', 'acute laryngitis' - Then read the relevant file blocks to extract detailed content - Also search paragraphs_fts for specific facts on each topic STEP 1: Search headings ```sql SELECT title, book_title, '/textbooks/' || block_file_path AS file_path, line_number, para_line_ranges, para_count FROM headings_fts WHERE headings_fts MATCH 'larynx OR laryngeal' ORDER BY rank LIMIT 20 ``` ```sql SELECT title, book_title, '/textbooks/' || block_file_path AS file_path, line_number, para_line_ranges, para_count FROM headings_fts WHERE headings_fts MATCH 'diphtheria OR laryngeal stenosis OR laryngeal edema' ORDER BY rank LIMIT 20 ``` STEP 2: Read the most relevant blocks found from headings search results. STEP 3: Search paragraphs_fts for specific content: ```sql SELECT book_title, section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end, snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 30) as snippet FROM paragraphs_fts WHERE paragraphs_fts MATCH 'laryngeal anatomy physiology' ORDER BY rank LIMIT 10 ``` ```sql SELECT book_title, section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end, snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 30) as snippet FROM paragraphs_fts WHERE paragraphs_fts MATCH 'laryngeal edema stenosis' ORDER BY rank LIMIT 10 ``` ```sql SELECT book_title, section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end, snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 30) as snippet FROM paragraphs_fts WHERE paragraphs_fts MATCH 'diphtheria larynx croup' ORDER BY rank LIMIT 10 ``` STEP 4: Read ALL relevant blocks fully (100 lines at a time). Return a comprehensive structured report with ALL details found, including: - Exact anatomy details (cartilages, muscles, ligaments, nerve supply, blood supply) - Physiology (voice production, respiration, swallowing protection) - Examination methods (laryngoscopy, stroboscopy, etc.) - Acute laryngitis (etiology, pathology, symptoms, treatment) - Laryngeal edema (types, causes, pathophysiology, clinical features, emergency management) - Laryngeal stenosis (classification, causes, degrees, clinical features, treatment) - Diphtheria of larynx (pathology, stages, clinical features, diagnosis, treatment) - Include book titles and page references for citations Return ALL the raw detailed content you find — do not summarize too briefly. The goal is comprehensive medical education content.

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Clinical anatomy, physiology and methods of larynx research. Acute diseases of the larynx. Laryngeal edema. Laryngeal stenosis. Diphtheria of the larynx. Explain in detail

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The Larynx: Clinical Anatomy, Physiology, Examination Methods, and Acute Diseases

I. CLINICAL ANATOMY OF THE LARYNX

Overview and Position

The larynx is a hollow musculoligamentous structure with a cartilaginous framework that caps the lower respiratory tract. Its cavity is continuous below with the trachea and opens above into the pharynx immediately posterior and slightly inferior to the tongue. It functions simultaneously as an airway valve (sphincter to close the lower respiratory tract) and a sound-producing organ.

The larynx is suspended from the hyoid bone above and attached to the trachea below by membranes and ligaments. It is highly mobile in the neck and can move up and forward (during swallowing) or down and backward. Motor and sensory innervation are provided by the vagus nerve [X].

— Gray's Anatomy for Students, p. 1192

Regions of the Larynx

The larynx is divided into three regions based on lymphatic drainage patterns:

Supraglottis — from the tip of the epiglottis to the top of the vocal folds (including the upper arytenoid). Contains the epiglottis, aryepiglottic folds, false vocal folds.
Glottis — from the top of the vocal folds to 1 cm below the top of the vocal folds. Contains the true vocal folds and the rima glottidis.
Subglottis — below the vocal folds to the first tracheal ring.

This three-part division is clinically significant because each region has different lymphatic drainage, influencing the pattern of spread of laryngeal malignancies and edema. — Murray & Nadel's Textbook of Respiratory Medicine, p. 1619

Cartilaginous Framework

The larynx is composed of three large unpaired cartilages, three pairs of smaller cartilages, and a fibro-elastic membrane:

Unpaired Cartilages:

1. Cricoid Cartilage

The most inferior laryngeal cartilage and the only one that completely encircles the airway.
Shaped like a signet ring: broad posterior lamina, narrow anterior arch.
The posterior lamina has two shallow oval depressions for the posterior cricoarytenoid muscles, separated by a vertical ridge for esophageal attachment.
Has articular facets for the arytenoid cartilages (superolateral) and inferior horns of the thyroid cartilage (lateral).
The cricoid is attached to the trachea by fibrous attachments inferiorly.

2. Thyroid Cartilage

The largest laryngeal cartilage. Formed by right and left laminae that converge anteriorly.
The superior fusion point projects forward as the laryngeal prominence (Adam's apple) — more prominent in men (angle ~90°) than women (~120°).
The superior thyroid notch is a palpable landmark just above the prominence.
Each lamina has a superior horn (connected to the greater horn of hyoid by the lateral thyrohyoid ligament) and an inferior horn (articulates with the cricoid).
The oblique line on the lateral surface is the attachment for sternothyroid, thyrohyoid, and inferior constrictor muscles.

3. Epiglottis

Leaf-shaped fibroelastic cartilage. Attached inferiorly to the thyroid angle by the thyroepiglottic ligament.
Attached to the hyoid bone by the hyoepiglottic ligament.
During swallowing, the epiglottis folds down over the laryngeal inlet to protect against aspiration.

Paired Cartilages:

Arytenoid Cartilages — Pyramid-shaped, articulate with the cricoid. Each has a vocal process (forward, for attachment of the vocal ligament) and a muscular process (lateral, for muscular attachment). Movements of the cricoarytenoid joint include gliding and rotation, enabling vocal fold abduction and adduction.

Corniculate Cartilages — Small, horn-shaped, sit atop the arytenoids. Visible as corniculate tubercles in the laryngeal inlet.

Cuneiform Cartilages — Club-shaped, embedded in the aryepiglottic folds. Visible as cuneiform tubercles at the laryngeal inlet margin.

— Gray's Anatomy for Students, p. 1193

Ligaments and Membranes

Thyrohyoid membrane — connects thyroid cartilage to hyoid bone. Pierced by the superior laryngeal artery and internal branch of the superior laryngeal nerve.
Cricothyroid ligament/membrane — connects thyroid to cricoid anteriorly. Site of emergency cricothyrotomy.
Cricothyroid joint — fibrous joint connecting thyroid and cricoid laterally.
Quadrangular membrane — internal membrane with its free lower margin forming the vestibular ligament (false vocal cord).
Conus elasticus (cricovocal membrane) — from cricoid upward; its superior free margin thickens to form the vocal ligament (true vocal cord).
Thyroepiglottic ligament — attaches epiglottis to thyroid angle.

Laryngeal Cavity

The cavity is divided into three chambers by the vestibular and vocal folds:

Vestibule — between the laryngeal inlet and the vestibular (false) folds.
Middle chamber (ventricle) — the narrow space between false and true folds. Laterally, the mucosa bulges out to form the laryngeal ventricle; an elongated extension forms the laryngeal saccule, lined by mucous glands that lubricate the vocal folds.
Infraglottic (subglottic) space — from the true vocal folds to the inferior laryngeal opening.

The rima glottidis (glottis) is the aperture between the two vocal folds. It is the narrowest part of the laryngeal cavity (and of the entire airway in adults). — Gray's Anatomy for Students, p. 1201

Intrinsic Muscles

All intrinsic muscles are innervated by the recurrent laryngeal nerve (branch of vagus [X]), except the cricothyroid, which is innervated by the external branch of the superior laryngeal nerve.

Muscle	Action
Posterior cricoarytenoid (PCA)	Abducts vocal folds (opens glottis) — the ONLY abductor
Lateral cricoarytenoid (LCA)	Adducts vocal folds (closes glottis)
Transverse arytenoid	Adducts arytenoids (closes posterior glottis)
Oblique arytenoids	Narrow the laryngeal inlet; constrict the distance between arytenoids and epiglottis
Thyroarytenoid	Shortens and relaxes the vocal folds (broad flat muscle lateral to laryngeal ventricle)
Vocalis	Fine tension adjustment of the vocal folds (runs parallel to vocal ligament)
Cricothyroid	Tilts cricoid backward relative to thyroid, elongating and tensing vocal folds (raises pitch)

— Gray's Anatomy for Students, p. 1202

Blood Supply

Superior laryngeal artery — from the superior thyroid artery (branch of external carotid); accompanies the internal branch of the superior laryngeal nerve through the thyrohyoid membrane; supplies the supraglottis.
Inferior laryngeal artery — from the inferior thyroid artery (thyrocervical trunk of subclavian); ascends with the recurrent laryngeal nerve; supplies the subglottis.

Venous drainage: Superior laryngeal veins → superior thyroid veins → internal jugular. Inferior laryngeal veins → inferior thyroid veins → left brachiocephalic vein.

Lymphatics: Above the vocal folds → deep cervical nodes (at carotid bifurcation). Below the vocal folds → pretracheal and paratracheal nodes. The vocal folds themselves have virtually no lymphatic drainage — a key reason early glottic carcinoma has an excellent prognosis.

— Gray's Anatomy for Students, p. 1206

Nerve Supply

Superior laryngeal nerve (SLN, from vagus [X]): divides into:
- Internal branch — sensory to the laryngeal mucosa above the vocal folds; enters larynx through thyrohyoid membrane.
- External branch — motor to the cricothyroid muscle.
Recurrent laryngeal nerve (RLN, from vagus [X]): motor to all other intrinsic laryngeal muscles; sensory to mucosa below the vocal folds. Ascends in the tracheoesophageal groove on each side.

II. PHYSIOLOGY OF THE LARYNX

The larynx serves three fundamental physiological functions:

1. Airway Protection (Sphincter Function)

The larynx acts as a valve to prevent aspiration. During swallowing, the larynx moves dramatically upward and forward, the epiglottis folds down over the inlet, the aryepiglottic folds constrict, and the true and false vocal folds adduct — providing three levels of closure. This multi-level closure is a coordinated reflex orchestrated by the brainstem. Laryngospasm is a protective reflex triggered by contact of foreign particles or liquid with the vocal folds or supraglottic structures, resulting in complete glottic closure. — Murray & Nadel, p. 1623

2. Respiration

The posterior cricoarytenoid muscles abduct the vocal folds, widening the rima glottidis to reduce airway resistance during inspiration. The glottis also regulates expiratory flow: partial adduction during expiration increases expiratory resistance and helps maintain PEEP (positive end-expiratory pressure), contributing to lung volume maintenance.

3. Phonation (Voice Production)

Phonation occurs when the vocal folds are adducted (closed) and air forced from the lungs causes them to vibrate. The fundamental frequency is determined by:

Vocal fold length and tension (controlled by cricothyroid and thyroarytenoid/vocalis muscles)
Subglottic air pressure
Vocal fold mass

The cricothyroid muscle elongates the folds (raising pitch); the vocalis relaxes them (lowering pitch). Resonance, articulation, and breath control shape the final voice.

In individuals receiving exogenous testosterone (e.g., as part of masculinizing hormone therapy), the vocal cords lengthen and thicken, lowering fundamental frequency and producing a masculinized voice. — Gray's Anatomy for Students, p. 1205

4. Expulsive Function

The larynx assists in coughing and Valsalva maneuver by allowing buildup of intrathoracic pressure (adducted cords) followed by explosive release.

III. METHODS OF LARYNX EXAMINATION

1. Indirect Laryngoscopy

A small rod-mounted mirror (similar to a dental mirror) is passed into the oropharynx. With adequate lighting and depression of the tongue, the examiner obtains an indirect mirror image of the larynx. This is an office-based, inexpensive technique. Limitations include gag reflex, poor visualization in some patients, and inability to assess dynamic function.

2. Direct Laryngoscopy

Performed using a rigid laryngoscope with a curved metal blade (Macintosh) or straight blade that lifts the tongue and epiglottis forward for direct visualization. Requires general anesthesia or topical anesthesia with absent gag reflex. Allows biopsy, foreign body removal, and surgical intervention. — Gray's Anatomy for Students, p. 1205

3. Flexible Fiberoptic Nasolaryngoscopy

Passage of a flexible fiberoptic endoscope through the nasal cavity into the hypopharynx. Considered the gold standard for bedside laryngeal assessment. Allows real-time dynamic assessment of vocal fold movement, paradoxical movement, lesions, secretions. Essential in evaluation of:

Hoarseness and dysphonia
Stridor
Dysphagia
Vocal fold paralysis
Laryngeal tumors

4. Microlaryngoscopy (Operative)

Microscope-assisted direct laryngoscopy under general anesthesia. Allows magnified visualization and microsurgical intervention on vocal folds (polyps, nodules, tumors).

5. Stroboscopy (Videostroboscopy)

Uses a stroboscopic light source synchronized to the vocal frequency to create a slow-motion optical illusion of vocal fold vibration. Essential for evaluating mucosal wave propagation and fine vocal fold pathology (early lesions, scarring).

6. Spirometry / Flow-Volume Loop

An essential functional test. Variable extrathoracic obstruction (e.g., vocal fold paralysis, paradoxical vocal fold motion) produces flattening of the inspiratory limb of the flow-volume loop. When maximal inspiratory flow falls below 1.5 L/sec, most patients are markedly symptomatic. — Murray & Nadel, p. 1623

7. Imaging

CT scan — evaluates cartilage integrity, soft tissue extent of lesions, lymphadenopathy, and laryngeal trauma.
MRI — superior soft tissue contrast.
Laryngeal fractures appear on CT as linear lucencies with displacement or distortion of cartilage (best seen on bone windows in ossified cartilage).

IV. ACUTE DISEASES OF THE LARYNX

Acute Laryngitis

Definition: Diffuse acute inflammatory swelling of the laryngeal mucosa, the most common cause of acute hoarseness.

Etiology:

Viral (most common): rhinovirus, parainfluenza, influenza, adenovirus — typically part of an upper respiratory tract infection.
Bacterial: less common; Streptococcus, Haemophilus influenzae.
Fungal (especially Candida albicans): occurs in immunocompromised patients, those on inhaled corticosteroids, or prolonged broad-spectrum antibiotics.
Irritants: cigarette smoke, chemical inhalation, gastroesophageal reflux (GERD).

Clinical Features:

Hoarseness (dysphonia), rough or breathy voice quality
Sore throat, odynophagia
Dry cough
Often associated with rhinorrhea, fever, malaise
Stridor and respiratory distress are uncommon in adults but can occur

Treatment:

Conservative: voice rest (avoid whispering, which strains the folds), adequate hydration, humidification, avoidance of cigarette smoke and irritants.
Antibiotics: not recommended for viral laryngitis. A Cochrane review concluded the risks of antibiotics outweigh the benefits. Consider only if strong evidence of bacterial superinfection.
Fungal laryngitis: Topical nystatin, miconazole, or clotrimazole; systemic fluconazole or ketoconazole for more severe cases.
Symptoms typically resolve within days for viral laryngitis. Persistent hoarseness beyond 3 weeks warrants laryngoscopy to exclude malignancy or other structural pathology.

— Textbook of Family Medicine 9e, p. 436

Acute Epiglottitis (Supraglottitis)

Definition: Rapidly progressive, potentially life-threatening bacterial infection of the epiglottis and supraglottic structures.

Etiology: Historically Haemophilus influenzae type b (Hib) in children; since widespread Hib vaccination, adult cases now predominate. Other organisms: Streptococcus pyogenes, S. pneumoniae, Staphylococcus aureus.

Pathophysiology: Infection causes massive edema of the epiglottis, aryepiglottic folds, and arytenoids, rapidly narrowing the supraglottic airway. The thickened epiglottis is visible on CT (Fig. 8.49 in Cummings).

Clinical Features:

Rapid onset of high fever, severe sore throat, dysphagia, drooling
Tripod position (leaning forward on hands, neck extended)
Muffled "hot potato" voice, stridor (inspiratory — obstruction above vocal folds)
"Thumbprint sign" on lateral neck X-ray (thickened epiglottis)

Management:

Airway is the priority — immediate preparation for intubation or surgical airway (tracheostomy).
IV antibiotics: ceftriaxone or ampicillin-sulbactam.
Corticosteroids (IV dexamethasone) to reduce edema.
Do NOT examine the throat in an uncontrolled setting in children — risk of precipitating complete obstruction.

Acute Subglottic Croup (Laryngotracheobronchitis)

Definition: Viral infection causing subglottic edema and narrowing, predominantly in children 6 months to 3 years.

Etiology: Parainfluenza virus (most common), RSV, influenza.

Clinical Features: Barking cough ("seal bark"), inspiratory stridor, hoarseness. Symptoms worse at night. Subglottic edema produces the classic "steeple sign" on AP neck X-ray.

Treatment: Humidified cool air; oral dexamethasone (single dose); inhaled racemic epinephrine for moderate-severe cases.

V. LARYNGEAL EDEMA

Definition and Pathophysiology

Laryngeal edema is abnormal accumulation of fluid in the loose submucosal connective tissue of the larynx. The supraglottic structures (epiglottis, aryepiglottic folds, false folds, arytenoids) are most susceptible because they contain abundant loose areolar connective tissue. The true vocal folds contain tightly bound epithelium (stratified squamous) and are less prone to edema, though Reinke's space (the superficial lamina propria) is the exception. The subglottis in children is particularly dangerous because the cricoid ring is inelastic and cannot expand to accommodate swelling.

Causes

Category	Examples
Allergic/Anaphylactic	Angioedema (C1-esterase inhibitor deficiency, drug-induced), bee sting, food allergy (nuts, shellfish)
Iatrogenic/Post-intubation	Prolonged intubation, repeated intubation, oversized ET tube
Infectious	Epiglottitis, Ludwig's angina, peritonsillar/retropharyngeal abscess with extension
Inflammatory	Gastroesophageal reflux laryngitis, irritant inhalation, radiation
Traumatic	Surgical manipulation, blunt/penetrating neck trauma
Neoplastic	Obstruction by laryngeal/hypopharyngeal tumors
Hereditary Angioedema (HAE)	C1-INH deficiency — recurrent episodes without urticaria

Clinical Features

Progressive hoarseness, dysphonia, muffled voice
Inspiratory stridor (supraglottic obstruction → inspiratory; subglottic → biphasic)
Dysphagia, drooling, sensation of throat tightening
Respiratory distress, accessory muscle use, suprasternal retractions
In severe cases: cyanosis, apnea, death

Emergency Management

Post-intubation/surgical laryngeal edema:

High-dose IV corticosteroids: dexamethasone 8 mg IV every 8 hours for 24–72 hours.
Humidified oxygen; nebulized racemic epinephrine.
Airway monitoring in ICU.

Anaphylactic angioedema:

Immediate epinephrine (IM adrenaline 0.3–0.5 mg, 1:1000)
IV antihistamines (chlorpheniramine), IV corticosteroids (hydrocortisone)
Secure the airway early (before complete obstruction)

Hereditary Angioedema:

C1-INH concentrate, icatibant (bradykinin B2 receptor antagonist), or ecallantide
Avoid ACE inhibitors (trigger bradykinin-mediated edema)

Airway rescue: If edema is progressing and intubation fails — emergency cricothyrotomy through the cricothyroid membrane (palpable landmark between thyroid and cricoid cartilages). This is life-saving and bypasses the glottic obstruction.

— Sabiston Textbook of Surgery, p. 1348; Gray's Anatomy for Students, p. 1193

VI. LARYNGEAL STENOSIS

Definition

Laryngeal stenosis refers to narrowing of the laryngeal lumen due to scarring, inflammation, or structural abnormality, leading to impaired airflow. It can be acute (e.g., edema, hematoma) or chronic (fibrotic scarring).

Classification by Site

Supraglottic stenosis — rare; usually due to trauma, burns, or radiation.
Glottic stenosis — involves the true vocal folds and interarytenoid region.
Posterior glottic stenosis (PGS) — most clinically important type; scarring of the posterior commissure and cricoarytenoid joints.
Subglottic stenosis — 1–3 cm below the glottis; common complication of prolonged intubation.
Combined/circumferential — multiple levels involved.

Causes

Cause	Mechanism
Prolonged intubation (most common)	ET tube pressure on posterior laryngeal mucosa → mucosal erosion → ulceration → scarring and fixation of cricoarytenoid joints
Repeated intubations	Cumulative mucosal trauma
Oversized ET tube	Excessive mucosal pressure
External laryngeal trauma	Blunt or penetrating injury, laryngeal fractures
Prior laryngeal surgery	Surgical scarring
Laryngeal infections	Diphtheria (membrane formation), epiglottitis
Inflammatory/autoimmune	Wegener's granulomatosis (GPA), relapsing polychondritis, sarcoidosis, amyloidosis
Congenital	Subglottic stenosis, laryngeal web
Radiation	Fibrosis after head and neck RT

Posterior Glottic Stenosis (PGS) — in Detail

This is the most common form of chronic laryngeal stenosis. When patients present with bilateral vocal fold immobility after prolonged intubation, 95% of the time the immobility is secondary to scar formation in and around the cricoarytenoid joints — not paralysis. The endotracheal tube rubs against the posterior laryngeal mucosa → erosion → inflammation → secondary infection and ulceration → granulation tissue → fibrosis → scar fixation of the joints.

GERD may contribute by adding additional mucosal irritation. — Murray & Nadel, p. 1625

Clinical Features

Slow progressive dyspnea on exertion (often misdiagnosed as asthma)
Inspiratory stridor (biphasic when subglottic)
Reduced exercise tolerance
Prolongation of inspiration on examination
Voice is often surprisingly preserved until late stages
When maximal inspiratory flow falls below 1.5 L/sec, patients are markedly symptomatic

Diagnosis

Flexible laryngoscopy — reveals vocal fold immobility or narrowed glottis/subglottis; also distinguishes scar from paralysis by probing the arytenoids.
Spirometry/flow-volume loop — flattening of the inspiratory limb (variable extrathoracic obstruction pattern).
CT or MRI of the larynx — evaluates extent of scarring, cartilage integrity.
If inspiratory flow ~2 L/sec — patient can manage modest activity (one flight of stairs, level walking).

Treatment

Medical: Anti-reflux therapy (PPI) to reduce mucosal irritation; treat contributing infection.

Surgical options (the goal is to enlarge the airway while preserving voice — "the great compromise"):

Transverse cordotomy or partial arytenoidectomy — removes the posterior vocal fold/arytenoid cartilage to enlarge the posterior airway by 1–2 mm. Trades airway for voice quality (breathy voice due to air leak).
Suture lateralization — sutures one or both vocal folds in abducted position; some techniques are reversible.
Botulinum toxin injection — into adductor muscles; reduces adductor force, allows abductors to function better; requires repeat injections.
Laser endoscopic procedures — CO₂ laser posterior cordectomy.
Tracheostomy — bypasses glottis; skin-lined stoma minimizes granulation tissue, allows one-way valve for phonation.
Experimental: Laryngeal pacemaker (electrical stimulation of posterior cricoarytenoid), surgical reinnervation of PCA muscle.

— Murray & Nadel's Textbook of Respiratory Medicine, p. 1625

VII. DIPHTHERIA OF THE LARYNX

Etiology and Organism

Diphtheria is caused by Corynebacterium diphtheriae, a gram-positive, unencapsulated, nonmotile, non-spore-forming bacillus. On microscopy it displays a characteristic club-shaped bacillary appearance and forms "Chinese character" patterns (palisades of parallel rods). The organism produces a potent protein exotoxin encoded by the tox gene, which is carried by corynebacteriophage β. Growth under iron-limiting conditions maximally expresses the toxin.

The toxin is an AB-type toxin: the B fragment binds host cells and facilitates entry of the A fragment, which irreversibly inactivates elongation factor EF-2 (by ADP-ribosylation), halting protein synthesis and causing cell death.

— Harrison's Principles of Internal Medicine, 22nd edition, p. 1265

Epidemiology

Transmitted via aerosol droplets; close contact required.
Incubation period: mean 1.4 days (up to 10 days).
Infectious period: ~18.5 days untreated; R₀ = 1.7–4.3.
Rare in countries with effective immunization (DTP vaccine). Sporadic outbreaks still occur in parts of Africa, Asia, Latin America, and in populations with incomplete vaccination coverage. Large-scale recent epidemics: post-Soviet states (1990s), Nigeria and Yemen (2022–2023).
Most common in winter months in temperate regions.
No significant animal reservoir — humans are the only host.

Pathology of Laryngeal (Respiratory) Diphtheria

Pseudomembrane formation is the hallmark:

The toxin causes coagulative necrosis of the mucosal epithelium.
Fibrin exudate, necrotic epithelium, inflammatory cells, and bacteria form a dense, adherent, grayish-white pseudomembrane over the pharynx, tonsils, and larynx.
The membrane is firmly adherent — attempts to remove it cause bleeding (distinguishes it from viral exudates which wipe off cleanly).
The membrane may extend from the pharynx into the larynx, trachea, and bronchi (membranous laryngotracheobronchitis — "descending croup").

Clinical Features — Laryngeal Diphtheria

Symptoms:

Onset is insidious; begins with hoarseness, a croupy (brassy) cough, low-grade fever, mild sore throat.
The characteristic "wet mouse" (or "sweetish") odor of the breath.
Hoarseness progresses to aphonia.
Inspiratory stridor develops as the membrane extends to the larynx and subglottis.
Patients have a toxemic appearance: pallor, prostration, weak pulse, cold extremities.
Bull neck appearance — due to cervical lymphadenopathy and soft tissue edema.

Diagnosis:

Clinical: presence of the characteristic grayish-white membrane; membrane bleeds when removal is attempted; "wet mouse" smell.
Microbiological: throat and nasopharyngeal swabs cultured on Löffler's medium (selective), Tinsdale's medium, or tellurite-containing agar. Diagnosis requires specific notation to the laboratory ("diphtheria suspected").
Toxin testing: Elek test (immunodiffusion) or PCR for the tox gene to distinguish toxigenic from nontoxigenic strains.
All toxigenic isolates must be reported to public health authorities.

— Harrison's Principles of Internal Medicine 22e, p. 1265; K.J. Lee's Essential Otolaryngology, p. 933

Complications

Complication	Timing	Mechanism
Airway obstruction	Days 1–14 (early)	Membrane extension to larynx/trachea; accounts for 60–65% of deaths
Toxic cardiomyopathy	1 week+	Toxin-mediated myocardial injury; arrhythmias, dilated cardiomyopathy; accounts for 20–25% of deaths
Polyneuropathy	3–5 weeks	Demyelination from toxin; begins with palatal, facial, and cranial nerve involvement; progresses to respiratory muscle weakness; reversible in survivors
Pneumonia	Concurrent	Secondary bacterial infection
Renal failure, encephalitis	Variable	Systemic toxin effects
Serum sickness	After antitoxin	Immune complex reaction to equine antitoxin

Children are particularly prone to airway obstruction because of their small airway diameters. — Harrison's, p. 1266

Treatment

1. Secure the airway — this is the immediate priority in laryngeal diphtheria.

Early intubation or tracheostomy before complete obstruction occurs.
Avoid forceful attempts to remove the membrane.

2. Diphtheria Antitoxin (DAT)

A horse-derived antiserum — the most critical intervention.
Must be administered as rapidly as possible after clinical diagnosis (do not wait for culture).
Neutralizes only unbound toxin — the sooner given, the better.
Test for horse serum hypersensitivity first (skin test); desensitization may be needed.
Dose varies by site, extent, and duration of disease (range: 20,000–120,000 units IV/IM).
Reduces local disease extent and complications (myocarditis, neuropathy).

3. Antibiotics

Penicillin G (IV/IM) or erythromycin for 14 days.
Antibiotics eliminate the organism (halting toxin production and transmission) but do not replace antitoxin.

4. Supportive Care

ICU monitoring for cardiac arrhythmias.
Cardiac monitoring (ECG) for myocarditis.
Respiratory support if polyneuropathy involves respiratory muscles.

5. Public Health

All close contacts: diphtheria toxoid booster + prophylactic penicillin or erythromycin.
Isolation of the patient.
Notification of public health authorities.

6. Prevention

DTP (diphtheria-tetanus-pertussis) vaccine: primary series in infancy (3 doses), boosters in childhood and every 10 years in adults (Td or Tdap).

— Harrison's Principles of Internal Medicine 22e, p. 1266–1267

Summary Table: Acute Laryngeal Diseases at a Glance

Disease	Key Pathogen	Hallmark Finding	Airway Risk	Priority Treatment
Acute viral laryngitis	Viruses (rhinovirus, parainfluenza)	Hoarseness, diffuse mucosal swelling	Low	Voice rest, hydration
Acute epiglottitis	H. influenzae b, Streptococcus	Thumbprint sign, tripod position	High	Airway first, IV ceftriaxone
Croup	Parainfluenza virus	Steeple sign, barking cough	Moderate	Dexamethasone, racemic epi
Laryngeal edema (anaphylactic)	Allergen trigger	Rapid onset, angioedema	Critical	IM epinephrine, airway
Laryngeal stenosis (post-intubation)	Scar from intubation	Bilateral immobility, inspiratory stridor	Chronic	Cordotomy/tracheostomy
Diphtheria	C. diphtheriae	Gray adherent pseudomembrane, bleeds on removal	High	Antitoxin + penicillin + airway

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