What is the difference between a macule and a papule?

Macule vs Papule: Key Differences and Clinical Significance

A macule is a flat, non-palpable discolored area of skin less than 1 cm in diameter, while a papule is a raised, palpable lesion less than 1 cm in diameter. 1

Defining Characteristics

Macules

• Appearance: Flat, non-elevated skin lesions
• Palpability: Non-palpable (cannot be felt when running finger over the skin)
• Size: Less than 1 cm in diameter
• Examples: Freckles, flat moles, petechiae, viral exanthems
• Clinical presentation: May appear as hyperpigmented, hypopigmented, or erythematous areas

Papules

• Appearance: Raised, solid skin lesions
• Palpability: Palpable (can be felt when running finger over the skin)
• Size: Less than 1 cm in diameter
• Examples: Acne, warts, lichen planus, early psoriasis lesions
• Clinical presentation: May be dome-shaped, flat-topped, or pointed

Clinical Significance

Diagnostic Implications

• The distinction between macules and papules is fundamental in dermatologic diagnosis and forms the basis of morphologic classification of skin lesions 1
• Correctly identifying whether a lesion is a macule or papule helps narrow the differential diagnosis
• Maculopapular rashes (containing both elements) are common in many conditions including drug reactions and viral exanthems 1

Examples in Clinical Practice

1. Immune-related cutaneous adverse events:

   • Non-specific maculopapular rashes are the most common skin manifestations of immune checkpoint inhibitor therapy 1
   • These typically occur within the first 6 weeks of therapy and involve <30% of body surface area 1

2. Infectious diseases:

   • In anthrax, cutaneous infection begins as a pruritic macule or papule that enlarges and ulcerates after 1-2 days 1
   • Viral exanthems often begin as macules that may evolve into papules

3. Severity assessment:

   • The CTCAE classification for rashes uses the extent of macules/papules to grade severity:
     • Grade 1: macules/papules covering <10% BSA
     • Grade 2: macules/papules covering 10-30% BSA
     • Grade 3: macules/papules covering >30% BSA 1

Clinical Evolution and Progression

Skin lesions may evolve from one morphology to another:

• Macules may develop into papules as inflammation progresses
• In Stevens-Johnson syndrome/toxic epidermal necrolysis, macules can evolve into vesicles and bullae 1
• In cutaneous mastocytosis, the most common presentation includes macules, plaques, or papules 1

Diagnostic Approach

When evaluating skin lesions:

1. Determine if the lesion is flat (macule) or raised (papule):

   • Use tangential lighting to enhance subtle elevation
   • Gently palpate the lesion with a gloved finger

2. Assess other characteristics:

   • Color (erythematous, hyperpigmented, hypopigmented)
   • Distribution pattern
   • Associated symptoms (pruritus, pain)
   • Evolution over time

3. Consider diagnostic tests when appropriate:

   • Skin biopsy for histopathologic examination
   • Wood's lamp examination for certain pigmentary disorders
   • Dermoscopy for detailed surface examination

Common Pitfalls

• Failing to use proper lighting when examining skin lesions
• Misclassifying slightly raised lesions as macules
• Not recognizing that lesions may have mixed characteristics (maculopapular)
• Overlooking subtle macules in fair-skinned individuals or papules in dark-skinned individuals

Remember that accurate identification of skin lesions as either macules or papules is the first step in dermatologic diagnosis and guides further evaluation and management of skin conditions.