What is the diagnosis and treatment for a patient presenting with erythematous rashes in the axilla (armpit), inguinal area (groin), neck, and hypogastric area (lower abdomen)?

Diagnosis and Management of Erythematous Rashes in Axilla, Inguinal, Neck, and Hypogastric Areas

Immediate Life-Threatening Exclusions

If fever, headache, or myalgia are present, initiate doxycycline 2.2 mg/kg orally twice daily immediately for presumed Rocky Mountain Spotted Fever (RMSF) without waiting for confirmation, as mortality reaches 20% if untreated and death can occur within 9 days. 1

• Query recent outdoor activities, tick exposure, and travel to endemic areas, noting that 40% of RMSF patients report no tick bite history and ticks preferentially attach in axillae and inguinal regions 1
• Consider concurrent ceftriaxone if meningococcemia cannot be excluded based on clinical presentation 1

Primary Diagnostic Algorithm

The distribution pattern you describe—axillae, inguinal area, neck, and hypogastric region—strongly suggests either an intertriginous dermatologic condition or a systemic histiocytic disorder rather than a typical infectious exanthem.

Step 1: Characterize the Rash Morphology

• Erythematous with scaling borders: Consider fungal infection (candidiasis, dermatophytosis) or inverse psoriasis 1
• Erythematous papular without scaling: Consider Langerhans Cell Histiocytosis (LCH), which presents as erythematous papular rash specifically in groin, abdomen, chest, or back 1
• Yellow-brown xanthomatous papulonodules: Consider Erdheim-Chester Disease affecting axillary and inguinal folds 1
• Red-to-brown macules or tender subcutaneous nodules: Consider Rosai-Dorfman Disease, which presents with these findings in 50% of patients 1

Step 2: Assess for Systemic Features

• Document presence of fever >38°C, which occurs in 75% of acute rheumatic fever cases but is less common in isolated dermatologic conditions 2
• Evaluate for lymphadenopathy, which suggests infectious etiology like erysipelas (present in 20-70% of cases) 3
• Check for muscle weakness, which combined with photosensitive rash on neck and torso suggests dermatomyositis 2

Step 3: Consider Specific Diagnoses Based on Location Pattern

For intertriginous involvement (axillae, inguinal, neck folds):

• Lupus erythematosus panniculitis can present as erythematous nodules and plaques specifically in axilla and inguinal regions, with annular configuration and parallel red lines at borders 4
• Drug-induced eczematous dermatitis from medications (particularly protease inhibitors) causes erythema and xerosis especially in skin folds, with neck and axillary creases particularly affected in over 90% of cases 2

Treatment Approach

For Fungal Infections (Most Common in These Locations)

• Apply topical antifungals to affected areas twice daily 1
• Keep skin folds completely dry with absorbent powder 1
• Change clothing daily and avoid occlusive garments 1
• Use low-potency hydrocortisone 1% only if significant inflammation present 1

For Inflammatory Dermatoses

• Apply low-potency hydrocortisone 1% to intertriginous areas (never high-potency steroids due to increased absorption and atrophy risk in axillae and groin) 1
• Prescribe oral antihistamines for pruritus control 1
• Avoid high-potency corticosteroids on face, genitalia, or skin folds 1

For Suspected Histiocytic Disorders

• Obtain tissue biopsy for definitive diagnosis of LCH, ECD, or RDD 1
• Perform comprehensive systemic evaluation including cardiac and pulmonary assessment for ECD 1

Critical Pitfalls to Avoid

• Never delay doxycycline if RMSF is suspected, as mortality increases dramatically with delayed treatment 1
• Never use high-potency corticosteroids in axillae or groin due to increased absorption and atrophy risk 1
• Never assume absence of tick bite excludes RMSF, as 40% of patients have no bite history 1
• Never apply occlusive dressings to intertriginous areas, as this promotes fungal and bacterial overgrowth 1

When to Escalate Care

• Rapid progression with fever >38.5°C, tachycardia >110 bpm, or extensive erythema >5 cm beyond initial margins requires hospitalization for aggressive bacterial infection 5
• Epidermal detachment or positive Nikolsky sign requires urgent dermatology consultation for Stevens-Johnson syndrome/toxic epidermal necrolysis 5
• Wooden-hard feel of subcutaneous tissues requires immediate surgical consultation for necrotizing fasciitis 5
• Grade 3 skin lesions (>50% body surface involvement) or suspicion of DRESS/SJS requires immediate discontinuation of all potentially causative medications and emergency hospitalization 2