COVID-19 AND SKIN DISEASE - Dermatology Notes
COVID-19 AND SKIN DISEASE - Dermatology Notes for Exams
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Introduction
COVID-19 is associated with a broad spectrum of cutaneous manifestations resulting from:
Viral cytopathic effects
Immune dysregulation
Cytokine-mediated inflammation
Vascular injury
Thrombotic microangiopathy
Drug reactions
Vaccine-induced immune activation
Cutaneous manifestations may:
Precede systemic symptoms
Occur during active infection
Appear during recovery
Reflect disease severity
A useful board-level classification divides lesions into:
Inflammatory/exanthematous eruptions
Vasculopathic/vasculitic lesions
Vaccine-associated eruptions
Hyperinflammatory syndromes (MIS-C/MIS-A)
FOUNDATIONS (First Principles)
Normal Cutaneous Immune Function
Skin contains:
Keratinocytes
Langerhans cells
Dermal dendritic cells
Endothelial cells
Resident T cells
Mast cells
Normal functions:
Antiviral defense
Cytokine signaling
Vascular regulation
Coagulation balance
SARS-CoV-2 Biology Relevant to Skin
SARS-CoV-2 enters cells through:
ACE2 receptor
TMPRSS2-mediated priming
Important pathogenic mechanisms:
Endothelial injury
Complement activation
Cytokine storm
Microvascular thrombosis
Interferon dysregulation
GENERAL PATHOGENESIS OF COVID-19 SKIN MANIFESTATIONS
Mechanisms
1. Viral-Induced Immune Activation
Produces:
Morbilliform eruptions
Urticaria
Vesicular eruptions
2. Endothelial Injury
Leads to:
Microthrombosis
Livedoid lesions
Retiform purpura
Necrosis
3. Type I Interferon Response
Associated with:
Pernio-like lesions (“COVID toes”)
Strong interferon responses may:
Limit viral replication
Produce chilblain-like inflammation
4. Hypercoagulability
Causes:
Vascular occlusion
Ischemic skin injury
1. COVID-19 TOES (PERNIO-LIKE / CHILBLAINS-LIKE LESIONS)
Definition
COVID-19 toes are acral erythematous-violaceous papules and plaques resembling chilblains.
Common in:
Children
Adolescents
Young adults
Usually associated with:
Mild or asymptomatic infection
Clinical Features
Violaceous papules on toes/fingers
Swelling
Burning or pain
Sometimes pruritus
Acral distribution
May develop:
Vesicles
Purpura
Erosions
Pathogenesis
Likely due to:
Robust type I interferon response
Endothelial inflammation
Microvascular injury
Not typically due to severe thrombosis.
HISTOPATHOLOGY
Findings
Superficial and deep lymphocytic infiltrate
Lymphocytic vasculitis
Papillary dermal edema
Endothelial swelling
Occasional thrombi
Histopathologic Logic
Interferon-driven inflammation targets:
Small acral vessels
Cold-sensitive acral circulation predisposes to injury.
Differential Diagnosis
Idiopathic chilblains
Lupus chilblains
Vasculitis
2. LIVEDO RETICULARIS (COVID-19-ASSOCIATED)
Definition
Livedo reticularis is a transient net-like violaceous discoloration caused by impaired cutaneous blood flow.
Usually indicates:
Mild vascular dysfunction
Clinical Features
Reticular violaceous pattern
Often transient
Symmetric
Trunk or extremities
Pathogenesis
Caused by:
Transient vasospasm
Low-grade vascular occlusion
Altered blood flow
Histopathology
May show:
Minimal vascular thrombosis
Mild endothelial injury
Prognosis
Usually associated with:
Mild disease
3. LIVEDO RACEMOSA (COVID-19-ASSOCIATED)
Definition
Livedo racemosa is a more irregular, broken, branching livedoid pattern.
Represents:
More severe vascular pathology
Clinical Features
Broken irregular violaceous network
More widespread
Persistent
Pathogenesis
Suggests:
Occlusive vasculopathy
Significant endothelial dysfunction
Histopathology
Vascular thrombosis
Endothelial swelling
Complement deposition
Clinical Importance
More strongly associated with:
Severe COVID-19
Hypercoagulability
4. RETIFORM PURPURA (COVID-19-ASSOCIATED)
Definition
Retiform purpura consists of branching purpuric plaques caused by occlusive vasculopathy.
Strongly associated with:
Severe disease
ICU patients
Pathogenesis
Severe endothelial injury activates:
Complement
Coagulation cascade
Results:
Microvascular thrombosis
Ischemia
HISTOPATHOLOGY
Key Features
Pauci-inflammatory thrombogenic vasculopathy
Dermal vessel thrombi
Complement deposition (C5b-9)
Minimal inflammation
Histopathologic Logic
This is primarily:
Thrombotic disease
rather than classic leukocytoclastic vasculitis.
Clinical Correlation
Retiform geometric morphology reflects:
Vascular territory infarction
5. CUTANEOUS NECROSIS (COVID-19-ASSOCIATED)
Definition
Cutaneous necrosis results from severe vascular occlusion and tissue infarction.
Clinical Features
Black eschar
Ulceration
Gangrene
Acral ischemia
Pathogenesis
Due to:
Disseminated thrombosis
Severe endothelial damage
Hypercoagulability
Histopathology
Epidermal necrosis
Vascular thrombi
Tissue infarction
Clinical Significance
Usually indicates:
Severe systemic disease
Poor prognosis
6. VESICULAR (VARICELLA-LIKE) ERUPTION
Definition
COVID-19-associated vesicular eruption consists of monomorphic vesicles resembling varicella.
Clinical Features
Truncal vesicles
Monomorphic lesions
Mild pruritus
Early manifestation possible
Pathogenesis
Possibly due to:
Viral cytopathic effect
Keratinocyte injury
HISTOPATHOLOGY
Findings
Acantholysis
Dyskeratosis
Intraepidermal vesiculation
Ballooning degeneration
Differential Diagnosis
Varicella
Grover disease
Drug eruption
7. MORBILLIFORM (MACULOPAPULAR) EXANTHEM
Definition
Morbilliform eruption is the most common COVID-related eruption.
Clinical Features
Erythematous macules and papules
Symmetric
Trunk predominant
Pruritic
Pathogenesis
Likely reflects:
Viral immune response
Cytokine-mediated inflammation
Drug hypersensitivity overlap
HISTOPATHOLOGY
Findings
Mild spongiosis
Superficial perivascular lymphocytes
Interface change occasionally
Eosinophils may suggest drug reaction
Differential Diagnosis
Drug eruption
Other viral exanthems
8. URTICARIAL ERUPTION
Definition
Urticaria may occur before or during COVID-19 infection.
Clinical Features
Transient wheals
Pruritus
Angioedema occasionally
Pathogenesis
Likely due to:
Mast cell activation
Cytokine release
Complement activation
HISTOPATHOLOGY
Findings
Dermal edema
Sparse perivascular infiltrate
Eosinophils variably
9. COVID-19 VACCINE-ASSOCIATED CUTANEOUS REACTIONS
Definition
Cutaneous immune reactions following COVID vaccination.
Associated with:
mRNA vaccines
Viral vector vaccines
A. LOCAL INJECTION SITE REACTION
Clinical Features
Pain
Erythema
Swelling
Mechanism:
Local innate immune activation
B. DELAYED LARGE LOCAL REACTION (“COVID ARM”)
Clinical Features
COVID arm:
Large erythematous plaque
Appears several days later
Pruritic/tender
Histopathology
Perivascular lymphocytes
Eosinophils
Mild spongiosis
Represents delayed hypersensitivity.
C. URTICARIA
May occur:
Immediately
Delayed
Mechanism:
Mast cell activation
D. MORBILLIFORM ERUPTION
Maculopapular exanthem after vaccination.
Often self-limited.
E. PITYRIASIS ROSEA-LIKE ERUPTION
Pityriasis rosea-like eruptions may occur after vaccination.
Possible mechanism:
Immune dysregulation
Viral reactivation
F. HERPES ZOSTER REACTIVATION
Herpes zoster reported after vaccination.
Likely reflects:
Temporary alteration in cell-mediated immunity
10. MIS-C (MULTISYSTEM INFLAMMATORY SYNDROME IN CHILDREN)
Definition
Multisystem Inflammatory Syndrome in Children is a postinfectious hyperinflammatory syndrome occurring weeks after infection.
Shares features with:
Kawasaki disease
Toxic shock syndrome
Cutaneous Findings
Polymorphous rash
Conjunctivitis
Strawberry tongue
Lip erythema/cracking
Acral edema
Perineal erythema/desquamation
Pathogenesis
Hyperinflammatory immune activation with:
Cytokine excess
Endothelial dysfunction
HISTOPATHOLOGY
Usually nonspecific:
Superficial perivascular inflammation
Endothelial activation
Clinical Importance
May involve:
Cardiac dysfunction
Shock
Coronary abnormalities
11. MIS-A (MULTISYSTEM INFLAMMATORY SYNDROME IN ADULTS)
Definition
Multisystem Inflammatory Syndrome in Adults is an adult hyperinflammatory syndrome occurring after COVID infection.
Cutaneous Findings
Morbilliform rash
Mucositis
Pernio-like lesions
Livedo
Retiform purpura
Pathogenesis
Similar to MIS-C:
Dysregulated postinfectious immune activation
HISTOPATHOLOGY
Variable depending on lesion type:
Vascular injury
Endothelial activation
Inflammatory infiltrates
PATTERN RECOGNITION & DIAGNOSTIC LOGIC
Pernio-like Lesions
Think:
Mild disease
Strong interferon response
Retiform Purpura / Necrosis
Think:
Severe COVID
Microthrombosis
Hypercoagulability
Morbilliform Eruption
Consider:
Viral exanthem
Drug eruption
Vesicular Eruption
Differentiate from:
Varicella
HSV
Grover disease
CLINICO-PATHOLOGICAL CORRELATION
Why COVID Toes Are Acral
Acral vessels are susceptible to:
Interferon-mediated vascular injury
Cold-associated microvascular dysfunction
Why Retiform Purpura Is Angulated
Vascular occlusion follows branching vessel territories.
Why Severe COVID Produces Necrosis
Extensive thrombosis causes tissue infarction.
Why Urticaria Is Transient
Histamine-mediated vascular permeability rapidly fluctuates.
MANAGEMENT
General Principles
Treat underlying COVID-19
Severity-based management
Symptomatic therapy
Pernio-like Lesions
Usually self-limited.
Treatment:
Topical corticosteroids
Warming measures
Urticaria
Antihistamines
Short corticosteroid courses occasionally
Morbilliform Eruption
Topical corticosteroids
Emollients
Evaluate medications
Vasculopathic Lesions
Require assessment for:
Coagulopathy
Systemic thrombosis
May require:
Anticoagulation
ICU care
MIS-C / MIS-A
Treatment may include:
IVIG
Systemic corticosteroids
Biologic immunomodulators
EXAM-FOCUSED INSIGHTS
Pernio-like lesions are associated with mild disease and strong interferon response.
Retiform purpura strongly correlates with severe COVID and thrombotic vasculopathy.
Complement-mediated endothelial injury is central in severe vasculopathic lesions.
Morbilliform eruption is the most common COVID-associated rash.
COVID vesicular eruption is monomorphic unlike classic varicella.
“COVID arm” is a delayed hypersensitivity reaction.
MIS-C resembles Kawasaki disease clinically.
Livedo racemosa suggests more severe vascular occlusion than livedo reticularis.
Retiform purpura is pauci-inflammatory thrombogenic vasculopathy rather than classic vasculitis.
Herpes zoster reactivation has been reported after vaccination.
MUST-KNOW BOARD EXAM QUESTIONS
1. Which COVID-associated lesion is linked to strong type I interferon response?
COVID toes (pernio-like lesions).
2. Which COVID skin manifestation is associated with severe thrombotic disease?
Retiform purpura.
3. What histopathologic feature characterizes severe COVID retiform purpura?
Pauci-inflammatory thrombogenic vasculopathy with vascular thrombi.
4. Which COVID eruption resembles varicella?
Monomorphic vesicular eruption.
5. What is the most common COVID-associated cutaneous eruption?
Morbilliform (maculopapular) exanthem.
6. Which vascular pattern indicates more severe vascular occlusion: livedo reticularis or livedo racemosa?
Livedo racemosa.
7. What is “COVID arm”?
Delayed large local hypersensitivity reaction after COVID vaccination.
8. Which syndrome resembles Kawasaki disease after COVID infection?
MIS-C.
9. What are classic mucocutaneous findings in MIS-C?
Conjunctivitis, strawberry tongue, lip erythema/cracking, polymorphous rash.
10. Which complement complex is implicated in severe COVID microvascular injury?
C5b-9 membrane attack complex.
11. Why does cutaneous necrosis occur in severe COVID?
Microvascular thrombosis and ischemic infarction.
12. Which histologic feature helps distinguish COVID retiform purpura from leukocytoclastic vasculitis?
Minimal inflammation despite extensive thrombosis.
13. What is the likely mechanism of COVID-associated urticaria?
Mast cell activation and cytokine release.
14. Which vaccine-associated eruption resembles pityriasis rosea?
PR-like papulosquamous eruption after COVID vaccination.
15. Which COVID-associated lesion is usually linked with mild disease and good prognosis?
Pernio-like (chilblains-like) lesions.