What are the differential diagnoses and treatment options for a raised rash in the axilla (armpit) area with irritation but no discharge?

Differential Diagnoses for Raised Axillary Rash with Irritation

The most common differentials for a raised, irritating rash in the axilla without discharge include contact dermatitis (irritant or allergic), atopic eczema, seborrheic dermatitis, intertrigo, folliculitis, and less commonly, early Lyme disease (erythema migrans) or drug-related eruptions.

Primary Differential Diagnoses

Contact Dermatitis (Irritant or Allergic)

• Most likely diagnosis in the axillary region given exposure to deodorants, antiperspirants, fragrances, and fabric softeners 1
• Presents as erythematous, raised lesions with pruritus and irritation 1
• Deterioration in previously stable skin may indicate development of contact dermatitis 1
• Consider recent changes in personal care products or detergents 1

Atopic Eczema/Dermatitis

• Commonly affects flexural areas including axillae 1
• Presents with itchy, erythematous, raised lesions with general dry skin 1
• May have personal or family history of atopic disease (asthma, hay fever) 1
• Secondary bacterial infection should be suspected if crusting or weeping develops 1

Seborrheic Dermatitis

• Can affect intertriginous areas including axillae 2
• Characterized by erythematous, scaly patches with irritation 2
• Associated with Malassezia yeast overgrowth 2

Folliculitis

• Presents as raised, erythematous papules or pustules around hair follicles 1
• Common in areas of friction and occlusion like axillae 1
• May be bacterial (Staphylococcus aureus) or fungal in origin 1

Intertrigo

• Inflammatory condition of skin folds including axillae 2
• Presents as erythematous, macerated patches with irritation 2
• Exacerbated by moisture, friction, and heat 2

Drug-Related Eruptions

• Papulopustular (acneiform) rash from EGFR inhibitors, MEK inhibitors, or mTOR inhibitors if patient is on cancer therapy 1
• Typically affects face, chest, and upper back but can involve axillae 1
• Presents as papules and pustules with pruritus or tenderness 1

Erythema Migrans (Early Lyme Disease)

• Consider if lesion is ≥5 cm and expanding 1
• Axilla is a common site for tick bites and erythema migrans 1
• Typically appears 7-14 days after tick bite (range 3-30 days) 1
• May be homogeneously erythematous or have central clearing 1
• Not scaly unless long-standing or topical corticosteroids have been applied 1

Key Diagnostic Considerations

Clinical Assessment Points

• Examine for distribution pattern: flexural involvement suggests atopic eczema; localized suggests contact dermatitis or folliculitis 1
• Assess for scaling: present in seborrheic dermatitis and atopic eczema; absent in early erythema migrans 1, 2
• Look for pustules or crusting: suggests secondary bacterial infection or folliculitis 1
• Measure lesion size: erythema migrans should be ≥5 cm for secure diagnosis 1
• Check for expansion: mark borders with ink and observe for 1-2 days; expanding lesions suggest erythema migrans 1

Important Pitfalls to Avoid

• Do not confuse tick bite hypersensitivity with erythema migrans: hypersensitivity reactions are usually <5 cm, may be urticarial, and disappear within 24-48 hours 1
• Do not overlook secondary bacterial infection: deterioration in stable eczema may indicate Staphylococcus aureus infection requiring bacterial culture and antibiotics 1
• Avoid applying topical corticosteroids before definitive diagnosis: this can mask erythema migrans and make it scaly 1

Initial Management Approach

For Suspected Contact or Atopic Dermatitis

• Identify and eliminate irritants: avoid deodorants, antiperspirants, fragrances, hot water, and harsh soaps 1
• Apply alcohol-free moisturizers with urea (5-10%) twice daily 1, 2
• Use low-potency topical corticosteroids (hydrocortisone 2.5% or alclometasone 0.05%) for axillary area to avoid skin atrophy 1, 3
• Avoid high-potency steroids in flexural areas due to increased risk of atrophy, striae, and telangiectasias 3

For Suspected Seborrheic Dermatitis

• Combine topical antifungal medications (to reduce Malassezia) with topical anti-inflammatory agents 2
• Use gentle, non-soap cleansers and avoid alcohol-containing preparations 2
• Apply moisturizers after bathing to provide surface lipid film 2

For Suspected Folliculitis

• Obtain bacterial culture if infection suspected (painful lesions, pustules, yellow crusts) 1
• Initiate oral antibiotics covering gram-positive organisms (doxycycline 100 mg twice daily or cephalexin 500 mg twice daily) for at least 14 days based on sensitivities 1

For Suspected Erythema Migrans

• Treat based on clinical findings without waiting for serologic confirmation, as serology is too insensitive in acute phase 1
• Initiate appropriate antibiotic therapy immediately if diagnosis is suspected 1

When to Obtain Cultures or Biopsy

• Bacterial swabs: if crusting, weeping, or failure to respond to initial treatment 1
• Skin biopsy: if diagnosis uncertain or no response to empiric treatment 1
• Viral culture/electron microscopy: if grouped, punched-out erosions suggest herpes simplex 1