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Desquamation
Desquamation refers to the loss of the outer skin layers due to epidermal cell breakdown and shedding. In dermatology and on exams, the term is used when the epidermis begins to peel or slough. This ranges from mild peeling in well-appearing patients to life-threatening epidermal detachment in critically ill patients.
Why it matters on exams:
• It is a “sick vs not sick” decision point
• Mucosal involvement, pain, and body surface area (BSA) predict severity
• Drug exposure within the past 1 to 3 weeks is a key trigger clue
• Misclassification leads to missed high-mortality diagnoses
Disorders in this category exist on a severity spectrum:
• Erythema multiforme (least severe)
• Stevens Johnson syndrome (intermediate, less than 10 percent BSA)
• Toxic epidermal necrolysis (most severe, greater than 30 percent BSA)
Erythema Multiforme (EM)
• Acute immune-mediated hypersensitivity reaction of the skin ± mucosa
• Most commonly triggered by HSV; can follow Mycoplasma pneumoniae
• Represents the mild end of the desquamation spectrum (vs SJS/TEN)
Clinical Presentation
Rash / Skin Findings
• Classic target or targetoid lesions with three distinct zones
• Acral distribution: hands, feet, forearms, face
• Symmetric pattern typical
• Minimal or absent mucosal involvement in EM minor
• No epidermal detachment or significant sloughing
Systemic Symptoms
• Mild or absent (possible low-grade fever or malaise)
• May follow herpes labialis or mild respiratory illness
The question stem would likely describe
• A well-appearing patient with target lesions on hands and feet after HSV lesions or atypical pneumonia symptoms
Diagnostics
• Clinical diagnosis
• HSV PCR or serology if recurrent pattern
• Mycoplasma workup if cough or atypical pneumonia present
• Medication review (less common trigger than in SJS/TEN)
Treatment
• Supportive care (topical corticosteroids, oral antihistamines)
• Discontinue possible triggers if identified
• EM major with mucosal involvement may require hydration and pain control
• Most cases resolve within 1 to 2 weeks
Stevens Johnson Syndrome (SJS)
• Severe mucocutaneous hypersensitivity reaction, usually medication-induced
• Less than 10 percent body surface area (BSA) epidermal detachment
• Shares a disease spectrum with toxic epidermal necrolysis (TEN)
• Potentially life-threatening, mortality higher than EM but lower than TEN
Clinical Presentation
Rash / Skin Findings
• Painful dusky erythematous or purpuric macules that may coalesce
• Blistering with progression to epidermal detachment
• Involves one or more mucosal surfaces (oral, ocular, genital)
• Positive Nikolsky sign may be present
(Nikolsky sign = gentle lateral pressure causes epidermis to shear or detach)
Systemic Symptoms
• Fever, malaise, photophobia, conjunctivitis
• Patients appear ill and may have significant discomfort from mucosal erosions
The question stem would likely describe
• A patient started on a high-risk medication (sulfa drugs, anticonvulsants, allopurinol, NSAIDs) who develops fever, painful rash, mucosal ulcerations, and early skin sloughing
Diagnostics
• Clinical diagnosis based on rash morphology, mucosal involvement, and BSA
• Basic labs to assess fluid, electrolyte, renal status
• Biopsy confirms full-thickness epidermal necrosis and separation, if uncertain
Treatment
• Immediate withdrawal of offending medication
• Hospital admission for close monitoring
• Supportive care is cornerstone: fluids, electrolytes, wound care, nutritional support, pain control
• Ophthalmology and urology/gynecology involvement for mucosal disease
• Consider ICU or burn unit transfer if progressing or severely ill
Toxic Epidermal Necrolysis (TEN)
• Life-threatening mucocutaneous hypersensitivity reaction, almost always medication-induced
• Greater than 30 percent body surface area (BSA) epidermal detachment
• Involves multiple mucosal surfaces (oral, ocular, genital)
• Causes severe pain, dehydration risk, and high mortality if not recognized quickly
• Requires ICU or burn unit–level supportive care
Clinical Presentation
Rash / Skin Findings
• Diffuse erythematous or purpuric patches that progress to blistering
• Full-thickness epidermal necrosis with sheet-like skin detachment
• Severe mucosal involvement is typical
• Positive Nikolsky sign
(Nikolsky sign = gentle lateral pressure causes epidermis to shear off)
Systemic Symptoms
• High fever, profound malaise, and severe skin pain
• Painful swallowing and ocular involvement are common
• Patients appear dehydrated, uncomfortable, and toxic
The question stem would likely describe
• A middle-aged patient who recently started a new medication (for example an anticonvulsant or antibiotic) with high fever, skin pain, mucosal erosions, and widespread sloughing
• The patient is unable to maintain oral intake and appears acutely ill
Diagnostics
• Clinical diagnosis based on morphology, BSA, and mucosal involvement
• Labs for fluid status, electrolytes, renal and hepatic function
• Monitor for secondary infection and sepsis
• Skin biopsy shows full-thickness epidermal necrosis and separation
Treatment
• Immediate withdrawal of the offending medication
• ICU or burn unit care for IV fluids, wound care, nutrition, and pain control
• Strict infection prevention and careful handling of fragile skin
• Ophthalmology evaluation due to high risk of ocular injury
• Supportive care is the cornerstone of management
Desquamation Exam Keys
Erythema Multiforme (EM)
Target or targetoid lesions, acral distribution, patient well-appearing, often HSV related, no skin sloughing.
Stevens Johnson Syndrome (SJS)
Fever and mucosal erosions with less than 10 percent body surface area detachment, medication trigger, patient ill.
Toxic Epidermal Necrolysis (TEN)
High fever, severe skin pain, mucosal erosions, more than 30 percent body surface area detachment, patient toxic-appearing.
Helpful Comparison Clues
• Minimal or no mucosa → think EM
• Mucosa + sick → think SJS or TEN
• Severe skin pain → strongly suggests TEN
• Nikolsky positive → SJS or TEN (not EM)
• Recent new medication (1 to 3 weeks) → SJS or TEN
• History of HSV → EM
Body Surface Area Breakdown
• EM: no significant detachment
• SJS: less than 10 percent
• SJS/TEN overlap: 10 to 30 percent
• TEN: greater than 30 percent
One-Line Differentiators
• EM = target lesions + healthy appearing
• SJS = mucosal disease + limited detachment
• TEN = mucosal disease + massive detachment + toxic appearing
Vesiculobullous Disorders
Vesiculobullous means “blister-forming.” These conditions make fluid-filled skin lesions (small = vesicles, larger = bullae). The big idea is whether the blisters are tight or fragile, and whether the mouth is involved.
Bullous Pemphigoid
• “Pemphigoid” comes from pemphix (blister) + -oid (looks like), meaning “blister-like.”
• Tense blistering disorder seen mostly in older adults; blisters stay intact and the mouth is usually spared
• Autoimmune reaction against hemidesmosomes (subepidermal split)
• Most common in elderly patients
Clinical Presentation
Rash / Skin Findings
• Large, tense bullae on an erythematous or urticarial base
• Blisters do not rupture easily
• Common on flexor surfaces, abdomen, and thighs
• Little to no mucosal involvement
Systemic Symptoms
• Pruritus may precede blisters
• Patients otherwise well-appearing
The question stem would likely describe
• An older adult with several weeks of itchy, tense blisters and no oral lesions
Diagnostics
• Clinical diagnosis is common
• Nikolsky sign negative (skin does not shear with pressure)
• Skin biopsy with direct immunofluorescence shows linear IgG and C3 at basement membrane
Treatment
• High-potency topical corticosteroids for limited disease
• Systemic corticosteroids or steroid-sparing agents for more extensive disease
• Goal is symptom control and prevention of new blisters
Pemphigus Vulgaris
• “Pemphigus” comes from pemphix (blister), referring to blister-forming diseases
• Flaccid blistering disorder with fragile bullae that rupture easily
• Prominent mucosal involvement (especially oral lesions)
• Autoimmune reaction against desmosomes (intraepidermal split)
• Can be life-threatening without treatment due to fluid loss and infection risk
Clinical Presentation
Rash / Skin Findings
• Flaccid, fragile bullae that break easily
• Painful erosions and crusting after bullae rupture
• Common on scalp, face, trunk, and mucosal surfaces
• Mucosal involvement is typical (oral ulcers common)
Systemic Symptoms
• Oral pain and difficulty eating or drinking
• Patients may appear uncomfortable due to painful erosions
The question stem would likely describe
• An adult with painful oral ulcers followed by fragile blisters on the skin that rupture easily
Diagnostics
• Clinical diagnosis supported by biopsy
• Nikolsky sign positive (skin shears with lateral pressure)
• Skin biopsy with direct immunofluorescence shows intercellular IgG in a “net-like” pattern
Treatment
• Systemic corticosteroids are first-line
• Steroid-sparing immunosuppressants (for example azathioprine, mycophenolate) often needed
• Early dermatology involvement recommended due to morbidity risk
Vesiculobullous Exam Keys
Bullous Pemphigoid
Tense blisters, elderly patient, minimal or no mucosa, subepidermal split, Nikolsky negative.
Pemphigus Vulgaris
Flaccid blisters, mucosal involvement (oral lesions common), intraepidermal split, Nikolsky positive.
Helpful Comparison Clues
• Tense = think pemphigoid
• Flaccid + mucosa = think pemphigus
• Elderly + pruritus before blisters = pemphigoid pattern
• Oral ulcers often come first in pemphigus vulgaris
• Nikolsky negative = pemphigoid
• Nikolsky positive = pemphigus vulgaris
• Basement membrane (linear IgG/C3) = pemphigoid
• Intercellular “net-like” IgG = pemphigus
