Diphtheria clinical features

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Diphtheria - Clinical Features

Causative Organism & Pathophysiology

Diphtheria is caused by Corynebacterium diphtheriae, an unencapsulated, non-motile, gram-positive bacillus. Toxigenic strains are lysogenized with a bacteriophage that produces an exotoxin which inhibits cellular protein synthesis (ADP-ribosylation of Elongation Factor-2). The toxin causes both local tissue necrosis (forming the pseudomembrane) and systemic effects on the heart, nervous system, and kidneys.

Incubation period: 2-4 days (range 1-8 days)

Types of Respiratory Diphtheria

1. Faucial (Pharyngeal/Tonsillar) Diphtheria

This is the most common and most toxic form.

Symptoms:

Sore throat (most frequent complaint)
Low-grade fever (high fever in severe/malignant forms)
Malaise, weakness, dysphagia, headache
Loss of appetite, voice changes
Cough, nasal discharge, neck edema (in <10% of patients)
Cervical adenopathy (in ~one-third of patients)

The Pseudomembrane (hallmark finding, present in >50% of patients):

Initially the pharynx appears erythematous
Grayish-white patches appear as necrosis begins, then coalesce
Evolves into a thick, grayish-black membrane with sharply defined borders
Adheres tightly to underlying tissue - bleeding occurs on attempted removal (key distinguishing feature)
Composed of: leukocytes, erythrocytes, fibrin, epithelial cells, and bacteria

Extent of membrane correlates with toxicity:

Membrane limited to tonsils = mild disease
Membrane covering entire pharynx = severe, abrupt onset

2. "Bull-Neck" / Malignant Diphtheria

Severe form with extensive cervical lymphadenopathy and neck tissue infiltration producing the classic "bull-neck" appearance. Clinical picture includes:

High fever
Severe muscle weakness
Vomiting, diarrhea
Restlessness and delirium
High risk of respiratory obstruction or cardiac failure

3. Nasal Diphtheria

Serous or serosanguineous (bloody) nasal discharge
Usually no constitutional symptoms
A membrane may be visible
Milder systemic toxicity

4. Laryngeal (Tracheobronchial) Diphtheria

May begin in the larynx or spread downward from the pharynx.

Classic "barking" cough
Hoarseness
Inspiratory stridor (may be paroxysmal and exhausting)
Dyspnoea/difficulty breathing
Marked edema of the neck ("bull neck")
Can progress to acute upper airway obstruction - a life-threatening emergency

Cutaneous Diphtheria

Skin ulcer with a grayish membrane
Clinically indistinguishable from other chronic skin lesions
Usually no systemic toxicity
Least toxic form; can act as reservoir and maintain carrier states

Systemic Complications (Toxin-Mediated)

Cardiac Complications

ECG changes of myocarditis in up to 65% of patients
Clinical myocarditis in 10-25% of cases
Onset: 1-2 weeks after illness (earlier in severe disease)
Manifestations: arrhythmias, heart block, congestive heart failure
Mortality rises to 7% with myocarditis and 26% with malignant/bull-neck form

Neurological Complications (Biphasic Pattern)

The neurological involvement follows a predictable biphasic sequence:

Early (Local) Phase - Weeks 1-3:

Finding	Timing
Palatal paralysis (most common - nasal voice, regurgitation, dysphagia)	Days 5-12
Other cranial nerve palsies (trigeminal, facial, vagus, hypoglossal)	Week 2-3
Ciliary body paralysis - loss of accommodation, blurred vision, preserved light reflex	Week 2-3

Delayed Phase - Weeks 5-8:

Sensorimotor polyneuropathy - ranges from mild distal polyneuropathy to rapidly ascending paralysis resembling Guillain-Barre syndrome
CSF findings similar to GBS: acellular fluid with elevated protein
Proximal muscles affected first; paralysis usually lasts <10 days but may persist up to 3 months
About 5% of respiratory infection patients develop polyneuritis; 75% of severe disease cases have some neuropathy

Key distinguishing neuropathy features:

Early oropharyngeal symptoms + ciliary paralysis with preserved pupillary light reflex + subacute delayed polyneuropathy = distinctive diphtheria pattern

Summary: Forms vs. Toxicity

Form	Toxicity	Key Feature
Pharyngeal	Highest	Gray pseudomembrane, bull neck
Laryngeal	High	Barking cough, stridor, airway obstruction
Nasal	Low	Serosanguineous discharge, no systemic symptoms
Cutaneous	Least	Ulcer with gray membrane

Overall Mortality

Overall: <3%
With myocarditis: ~7%
Malignant (bull-neck) form: ~26%
Death results from airway obstruction, cardiac failure (myocarditis), or respiratory failure from diaphragmatic paralysis

Sources: Rosen's Emergency Medicine, 9th Ed.; Tintinalli's Emergency Medicine, 9th Ed.; Scott-Brown's Otorhinolaryngology Head & Neck Surgery; Adams and Victor's Principles of Neurology, 12th Ed.

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