What causes trunk dermatosis?

Causes of Trunk Dermatosis

Trunk dermatosis encompasses a broad spectrum of conditions with diverse etiologies including inflammatory dermatoses (eczema, seborrhea, psoriasis), infectious causes (fungal, bacterial, parasitic), contact dermatitis, and rare acantholytic disorders—each requiring specific identification based on clinical presentation and associated features.

Inflammatory Dermatoses

The most common causes of trunk dermatosis are inflammatory skin conditions:

Eczema (Atopic Dermatitis)

• Presents with chronic pruritus typically starting in childhood with involvement of multiple body areas including the trunk 1
• Skin lesions demonstrate erythema, xerotic scaling, lichenification, and hyperpigmentation depending on disease stage 1
• Management includes gentle skin care, emollients, topical corticosteroids, and antipruritics 1

Seborrheic Dermatitis

• Common condition affecting sebaceous areas including the trunk, presenting with greasy yellowish scaling, itching, and secondary inflammation from Malassezia yeast 1
• More pronounced in patients with Down syndrome, HIV infection, and Parkinson's disease 1
• Treatment includes topical antifungal medications to reduce yeast and topical anti-inflammatory agents 1

Psoriasis

• Well-demarcated erythematous plaques with silvery-white scale, typically symmetrically distributed on trunk, elbows, and knees 2
• May include nail pitting or onycholysis and variable pruritus 2
• Treatment involves topical corticosteroids, vitamin D analogues, and dermatology referral if extensive 2

Contact Dermatitis

Irritant Contact Dermatitis

• Inflammation from direct chemical damage (acids/alkalis) causing erythema, edema, scaling, itch, and occasional pain 1
• All individuals susceptible in dose-dependent manner 1

Allergic Contact Dermatitis

• Occurs only in susceptible individuals with predisposition to allergens (metals, chemicals, cosmetics, soaps, plastics) 1
• Nickel is most common contact allergen, affecting approximately 10% of women with pierced ears 1

Infectious Causes

Fungal Infections

• Tinea versicolor presents as pink spots or hypopigmented patches on trunk in immunocompetent patients 3
• Dermatophyte infections can affect trunk, particularly in athletes with increased sweating and trauma 1
• Concurrent tinea pedis should be treated to prevent recurrence 2

Parasitic Infections

Larva Currens (Strongyloides stercoralis)

• Itchy, linear, urticarial rash moving 5-10 cm per hour, most commonly on trunk, upper legs, and buttocks 1, 4
• Associated with subcutaneous larval migration 1
• Treatment with ivermectin 200 μg/kg for 2 days 1

Onchocerciasis (Onchocerca volvulus)

• Diffuse dermatitis with severe pruritus on trunk and extremities, with nodules (onchocercoma) on bony prominences, head, and trunk 1
• Incubation period 8-20 months after black fly bite 1
• Treatment requires specialist input with doxycycline and ivermectin 1

Schistosomiasis

• Swimmers' itch/cercarial dermatitis presents as itchy maculopapular rash on trunk after freshwater exposure 1
• Resolves spontaneously over days to weeks 1

Bacterial Infections in Immunocompromised Hosts

• Gram-negative infections can present as erythematous maculopapular lesions, focal cellulitis, or cutaneous nodules on trunk 1
• Ecthyma gangrenosum preferentially found in groin, axilla, or trunk in neutropenic patients 1
• More than 20% of chemotherapy-induced neutropenic patients develop skin and soft-tissue infections 1

Rare Acantholytic and Specific Dermatoses

Transient Acantholytic Dermatosis (Grover's Disease)

• Benign, non-familial disorder presenting as polymorphous, pruritic lesions on trunk of unknown etiology 5, 6
• Can present as erythematous plaque variant 6
• Treatment with retinoids (acitretin) and dapsone as maintenance 5

Ashy Dermatosis

• Asymptomatic, symmetrically-distributed, gray-colored macules on trunk, neck, face, and upper extremities 7
• Most common in Fitzpatrick phototype III-V skin 7
• Etiology unknown but drug ingestion, infection, and genetic factors suggested 7
• Most successful treatment is clofazimine 7

Subcorneal Pustular Dermatosis (Sneddon-Wilkinson Disease)

• Rare, benign yet relapsing pustular dermatosis presenting as hypopyon pustules on trunk and intertriginous areas 8
• Dapsone remains first-line treatment 8

Keratosis Lichenoides Chronica

• Rare dermatosis with seborrheic dermatitis-like facial eruption plus violaceous papular and nodular lesions on trunk arranged in linear and reticulate pattern 9
• Responds partially to oral isotretinoin 9

Critical Clinical Pitfalls

In immunocompromised patients (neutropenia, chemotherapy, HIV, transplant recipients), any trunk rash requires urgent evaluation with blood cultures and tissue sampling, as benign-appearing lesions may represent disseminated infection 3. Rapidly progressive or necrotic lesions demand immediate assessment 3. Always examine for concurrent tinea pedis when trunk dermatosis is present, as this predisposes to recurrent infections 2.