What are the possible causes of bilateral erythema and pruritus with 0.2 cm papular lesions on the palms, soles, and axillae?

Differential Diagnosis of Bilateral Palmoplantar and Axillary Pruritic Papular Eruption

The combination of bilateral 0.2 cm pruritic papular lesions on palms, soles, and axillae most likely represents either palmoplantar psoriasis with inverse (flexural) involvement, dyshidrotic eczema (pompholyx), or—if acute onset—secondary syphilis, which must be excluded immediately with serologic testing. 1, 2

Immediate Life-Threatening Exclusions

Rule Out Secondary Syphilis First

• Obtain RPR or VDRL plus a treponemal-specific assay (e.g., TP-PA, FTA-ABS) immediately in any patient with symmetric palmoplantar papular lesions, because secondary syphilis classically presents with red-brown macules or papules on palms and soles and can involve axillae. 1, 2
• If serologies confirm syphilis, treat with benzathine penicillin G 2.4 million units intramuscularly as a single dose, perform HIV screening (syphilis and HIV frequently coexist), and notify sexual partners. 2
• Do not assume "simple dermatitis" without serologic exclusion—missing secondary syphilis leads to significant individual and public-health morbidity. 1

Assess for Tick-Borne Illness if Fever Present

• If the patient has fever, headache, or recent tick exposure, obtain a complete blood count to detect thrombocytopenia and initiate empiric doxycycline immediately for suspected Rocky Mountain spotted fever (RMSF), which presents with maculopapular rash spreading to palms and soles 2–4 days after fever onset and carries 5–10% mortality if untreated. 1
• Half of RMSF deaths occur within the first 9 days; delayed therapy markedly increases mortality. 1

Most Likely Dermatologic Diagnoses

Palmoplantar Psoriasis with Inverse Psoriasis

• The simultaneous involvement of palms, soles, and axillae strongly suggests psoriasis, because the disease frequently affects both palmoplantar and flexural (inverse) regions together. 3
• Palmoplantar psoriasis appears as well-demarcated erythematous plaques with silvery scale, thick hyperkeratosis, and fissuring; it is intensely pruritic despite small body-surface-area involvement. 4, 1, 3
• Inverse psoriasis in the axillae presents as erythematous plaques with minimal scaling in intertriginous folds. 3
• Look for additional psoriatic features: nail pitting, onycholysis, subungual hyperkeratosis, "oil-drop" sign, or plaques on scalp, elbows, knees, or genitalia. 3
• Query personal or family history of psoriasis or other autoimmune disorders. 3

Dyshidrotic Eczema (Pompholyx)

• Intensely pruritic vesicles (not just papules) confined to the lateral fingers, palms, and soles, often lasting about 3 weeks per flare, are characteristic of pompholyx. 1
• Pompholyx is strongly associated with atopic diathesis and hyperhidrosis. 1
• Axillary involvement is less typical for isolated dyshidrotic eczema; if present, consider concurrent irritant contact dermatitis from deodorants or clothing. 3
• Antihistamines are ineffective for pompholyx because it is not IgE-mediated. 1

Irritant Contact Dermatitis

• Frequent hand washing (especially during COVID-19 precautions), water temperature >40°C, or occupational chemical exposure can cause erythema, scaling, and pruritus on palms. 3
• Axillary involvement may result from deodorants or clothing irritants, but the symmetric palmoplantar-axillary distribution is less typical for pure contact dermatitis. 3

Rare Considerations

• Lichen planus: Highly pruritic erythematous to violaceous hyperkeratotic papules on palms and soles; look for typical violaceous papules with Wickham striae on wrists, legs, or oral mucosa. 5
• Papular purpuric gloves and socks syndrome (PPGSS): Painful or pruritic edema, erythema, petechiae, and purpura of palms and soles (usually with dorsal hand/foot extension); associated with parvovirus B19 or EBV; self-limited. 6
• Mycosis fungoides palmaris et plantaris: Rare cutaneous T-cell lymphoma mimicking dyshidrotic eczema; suspect if lesions persist despite topical corticosteroids. 7

First-Line Treatment Approach (Assuming Psoriasis or Eczema)

Intensive Topical Therapy for 8–12 Weeks

• Apply clobetasol propionate 0.05% cream or ointment twice daily under occlusion (plastic wrap, gloves, or socks overnight) to palms and soles. 4, 1, 3, 2
• Apply a moderate-potency corticosteroid (e.g., triamcinolone 0.1%) to axillae to avoid excessive absorption and skin atrophy in intertriginous zones. 3
• Combine with calcipotriene ointment or tazarotene gel on palmoplantar lesions for synergistic efficacy. 2
• Use urea 10% cream three times daily (including after hand washing) to provide keratolytic and humectant effects. 1
• Employ the "soak-and-smear" technique: soak hands/feet in plain water for ~20 minutes, then immediately apply thick moisturizer to damp skin to enhance drug penetration. 1

Identify and Eliminate Irritants

• If contact dermatitis is suspected, identify and remove offending agents (soaps, chemicals, deodorants); apply moisturizer after every hand wash using lukewarm water. 3

Second-Line Therapy: Phototherapy (If No Response After 4 Weeks)

• Soak PUVA (psoralen immersion of hands/feet followed by UVA exposure) 2–3 times weekly for several months achieves clearance in 58–81% of dyshidrotic eczema and 50–67% of hyperkeratotic eczema; the risk of cutaneous malignancy on palms/soles is very rare. 4, 1, 2
• Narrowband UVB or 308-nm excimer laser can be used for localized lesions when PUVA is unsuitable. 4, 1, 2

Third-Line Therapy: Systemic Agents (Severe or Refractory Disease)

Oral Acitretin (First-Line Systemic for Palmoplantar Psoriasis)

• Acitretin 25 mg orally daily produces substantial improvement (reduced scaling, thickness, erythema) within approximately 2 months. 4, 1, 3, 2
• After disease control, taper to 25 mg on alternate days to maintain benefit. 4
• Monitor lipid profile and liver enzymes every 1–2 months; manage hypertriglyceridemia with fibrates and hypercholesterolemia with statins, but never combine both agents concurrently due to rhabdomyolysis risk. 1, 2

Alternative Systemic Agents

• Methotrexate 15–25 mg orally weekly requires baseline and periodic liver-function tests and complete blood counts to monitor for hepatotoxicity and bone-marrow suppression. 1, 2
• Cyclosporine 2.5–5 mg/kg orally daily (limit ≤1 year) requires regular renal-function and blood-pressure monitoring due to nephrotoxicity risk. 1, 2

Fourth-Line Therapy: Biologic Agents (Refractory Palmoplantar Psoriasis)

• IL-17, IL-12/23 (ustekinumab), or IL-23 inhibitors are preferred over TNF-α blockers because head-to-head trials demonstrate higher skin-clearance rates. 1, 2
• For patients >100 kg, ustekinumab 90 mg subcutaneously at baseline, week 4, then every 12 weeks achieves 67% complete clearance of palmoplantar lesions (vs. 9% with 45 mg dose). 1
• TNF-α inhibitors (adalimumab, infliximab) remain effective but may paradoxically induce pustular psoriasis of palms/soles in approximately 1–2% of treated patients, even without prior psoriasis history. 4, 1, 2

Common Pitfalls

• Avoid systemic corticosteroids as monotherapy in psoriasis—they can precipitate severe flares, including life-threatening generalized pustular psoriasis. 1, 2
• Do not delay syphilis testing—assuming simple dermatitis without serologic exclusion can lead to significant morbidity. 1, 2
• Recognize that palmoplantar involvement, although limited in surface area, disproportionately impairs quality of life; systemic therapy is justified when topical measures fail. 4, 1, 3, 2

Indications for Dermatology Referral

• Failure of intensive topical therapy after 8–12 weeks of occlusive super-potent corticosteroids. 1
• Need for systemic agents (acitretin, methotrexate, cyclosporine) or biologic therapy. 1, 2
• Consideration of phototherapy (soak PUVA, narrowband UVB, excimer laser). 1, 2
• Persistent lesions despite treatment, raising concern for mycosis fungoides or other rare diagnoses. 7