What is the diagnosis and treatment for large brown spots with red spots in them on the chest, arms, and legs?

Differential Diagnosis: Large Brown Spots with Red Spots

The clinical description of large brown spots with red spots on the chest, arms, and legs is most consistent with pigmented purpuric dermatosis (PPD), specifically Schamberg disease, which presents as brown pigmentation with characteristic "cayenne pepper" or red spots on their edges. 1, 2

Primary Diagnostic Consideration: Pigmented Purpuric Dermatosis

Pigmented purpuric dermatosis should be your leading diagnosis based on the distribution and morphology described. 1

Clinical Features Supporting This Diagnosis:

• Brown macules or patches with overlying red "pepper spots" are pathognomonic for PPD 1, 2
• Distribution on chest, arms, and legs is typical, though lower extremities are most commonly affected 2
• The red spots represent petechiae (cayenne pepper-like spots) within the brown hyperpigmented areas 1, 2

Diagnostic Confirmation:

• Skin biopsy is required for definitive diagnosis when clinical presentation is atypical or diagnosis uncertain 2
• Histopathology will show superficial perivascular lymphocytic infiltrate with erythrocyte extravasation and hemosiderin deposition 2
• The brown color results from hemosiderin deposition, while red spots are extravasated erythrocytes 1, 2

Critical Alternative Diagnoses to Exclude

Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN)

This is a life-threatening emergency that must be ruled out immediately if the patient has systemic symptoms or mucosal involvement. 3

• SJS/TEN presents with purpuric macules or flat atypical targets with a dark red center surrounded by a pink ring 3
• Key distinguishing features: skin tenderness, positive Nikolsky sign, mucosal involvement (eyes, mouth, genitalia), and recent drug exposure 3
• If blistering, skin shearing, or mucosal erosions are present, this is a medical emergency requiring immediate hospitalization 3

Congenital Melanocytic Nevi (CMN)

Consider if lesions have been present since birth or early infancy. 3

• CMN present as brown patches with possible red-pink ("amelanotic") papules within them 3
• Multiple CMN with satellite lesions on trunk and extremities can occur 3
• These are congenital, not acquired, which distinguishes them from PPD 3

Melanoma

Any progressive change in size, shape, or color of pigmented lesions requires urgent evaluation. 4, 5

• Complete excision with 2mm margin is mandatory for any suspected malignant melanocytic lesion 4, 5
• Regional lymph node examination is essential 4
• However, melanoma typically presents as a single changing lesion, not multiple brown spots with red spots 4

Diagnostic Algorithm

Step 1: Assess for Emergency Features

• Check for skin tenderness, blistering, or positive Nikolsky sign (suggests SJS/TEN) 3
• Examine all mucous membranes (mouth, eyes, genitalia) for erosions 3
• If present, immediate hospitalization is required 3

Step 2: Determine Lesion Chronology

• Ask if lesions were present at birth (suggests CMN) 3
• Document if lesions are progressive or changing (raises melanoma concern) 4
• PPD typically develops gradually over weeks to months 1, 2

Step 3: Examine Lesion Morphology

• Look for "cayenne pepper spots" (red petechiae) within brown patches - diagnostic of PPD 1, 2
• Check for target-like lesions with central dusky red areas (suggests SJS/TEN) 3
• Assess for uniform brown color with overlying red-pink papules (suggests CMN) 3

Step 4: Perform Skin Biopsy

• Biopsy is required when clinical diagnosis is uncertain 2
• Use surgical knife, not laser or electrocautery, to preserve tissue architecture 4, 5
• For PPD: expect perivascular lymphocytic infiltrate with erythrocyte extravasation and hemosiderin 2

Treatment for Pigmented Purpuric Dermatosis

PPD is typically a benign, chronic condition that may not require treatment if asymptomatic. 1

Management Approach:

• Reassurance that this is a benign condition is often sufficient 1
• Topical corticosteroids can be used for symptomatic relief if pruritus is present 1
• Avoid trauma to affected areas, as this can worsen petechiae 2
• Monitor for progression, though spontaneous resolution can occur 1

Common Pitfalls to Avoid

• Do not assume all brown spots with red areas are benign without proper evaluation 4, 1
• Never use laser or electrocautery for initial biopsy of uncertain lesions, as this destroys diagnostic tissue 4, 5
• Do not miss SJS/TEN by failing to check for mucosal involvement and skin fragility 3
• Avoid partial biopsies when melanoma is in the differential - always perform complete excision with margins 4, 5
• Remember that PPD on upper extremities and trunk is less common but well-documented 2