Eczema Coxsackium

Eczema coxsackium is a distinctive clinical entity that emerged with the global spread of coxsackievirus A6 (CVA6) since 2008-2010 (first major outbreak Finland 2008, then global spread including Asia, Europe, North America). CVA6 has largely replaced the classic causes of hand-foot-and-mouth disease (HFMD) — coxsackievirus A16 and enterovirus 71 — as the predominant strain in many countries. The clinical presentation of CVA6 differs significantly from classic HFMD: it produces more extensive, atypical lesions that can mimic varicella, eczema herpeticum, or other vesicular eruptions. Eczema coxsackium specifically refers to the syndrome of atypical CVA6 hand-foot-and-mouth disease in patients with pre-existing atopic dermatitis (eczema), where the virus preferentially infects and spreads through eczematous skin. The pathophysiology involves disruption of the skin barrier in atopic dermatitis (filaggrin mutations, increased transepidermal water loss, altered tight junctions, decreased antimicrobial peptides), allowing easier viral access and spread. This is analogous to eczema herpeticum (HSV in atopic dermatitis), eczema vaccinatum (smallpox vaccinia virus historically), and other epidermal viral infections preferring atopic skin (Kaposi varicelliform eruption is the umbrella term).

Clinical presentation: most commonly affects young children (peak ages 6 months to 5 years) with established atopic dermatitis, although adults can be affected. Onset typically 3-6 days after viral exposure (close contact with infected child, daycare outbreak). Prodrome of fever (often high, 38.5-40°C), malaise, sore throat, decreased oral intake. Skin manifestations: classic HFMD features including vesicles on palms and soles, oral ulcers (mouth, tongue, buccal mucosa), and gluteal area lesions. ATYPICAL features in eczema coxsackium include extensive vesicular and vesiculobullous eruption in areas of pre-existing eczema (especially flexural — neck folds, antecubital and popliteal fossae, periorbital, perioral), perioral and chin involvement, trunk and extremity involvement beyond hands and feet, lesions may be larger (5-15 mm), more numerous, hemorrhagic, vesiculobullous, or purpuric than classic HFMD. Lesions are often more painful and pruritic than classic HFMD. Crusting and secondary bacterial infection (impetiginization with Staphylococcus aureus or Streptococcus pyogenes) is common. Petechiae and purpura over eczematous areas. Differential diagnosis: eczema herpeticum (HSV-1 in eczema, more painful, monomorphic punched-out vesicles, requires acyclovir), eczema vaccinatum (rare, smallpox vaccine contact), varicella (chickenpox, more disseminated, distinct lesions), atypical erythema multiforme, drug eruption, and disseminated impetigo. The history of pre-existing atopic dermatitis with sudden widespread vesicular eruption following febrile illness with classic HFMD features (palms, soles, mouth) suggests eczema coxsackium.

Diagnosis: primarily clinical based on classic HFMD features (palmoplantar and oral lesions) plus extensive eruption in eczematous areas. Confirmatory testing if uncertain: viral PCR from vesicle fluid or stool/throat swab can identify CVA6 (NOT routinely available in all settings); serology not routinely useful. If eczema herpeticum is in differential (especially with severe disease), HSV PCR or Tzanck smear (multinucleated giant cells) is essential — eczema herpeticum requires urgent IV acyclovir while eczema coxsackium does not. Workup: complete blood count (often normal or mild leukocytosis), wound cultures if suspected secondary bacterial infection. Course: most cases self-limited with resolution in 7-14 days. High fever may persist 3-5 days. Skin lesions resolve with desquamation. Onychomadesis (proximal nail matrix arrest causing horizontal nail shedding) develops in 30-60% of cases 4-8 weeks after infection — characteristic delayed signal of CVA6, with eventual normal nail regrowth (no permanent damage). Beau lines (transverse depressions in nail) may also develop. Complications: secondary bacterial superinfection (impetiginization 30%), dehydration from oral ulcers, rare central nervous system involvement (encephalitis, aseptic meningitis), rare cardiac involvement (myocarditis, very rare with CVA6 compared with EV71). Treatment: supportive care is mainstay. (1) Hydration (oral fluids, IV if needed for severe oral ulcers and dehydration). (2) Pain control (acetaminophen, ibuprofen, topical lidocaine for oral ulcers). (3) Cool compresses, calamine lotion for itching. (4) Continue baseline atopic dermatitis treatment but moderate-potency topical corticosteroids may be cautious during acute phase due to potential viral spread. Some authorities recommend stopping topical steroids during acute phase, others continue at lower potency. (5) Treat secondary bacterial infection with topical or systemic antibiotics. (6) Antiviral therapy (acyclovir) is NOT effective for coxsackievirus and is reserved for confirmed eczema herpeticum. (7) Patient and family education on transmission prevention (hand hygiene, isolation from other children, daycare exclusion until acute symptoms resolve). (8) Inform parents about delayed onychomadesis (4-8 weeks later) so they understand it represents prior infection, not new disease. (9) Optimize ongoing atopic dermatitis management to reduce future risk of similar epidermal viral infections — emollients, identification and treatment of flares. Recovery is generally complete in immunocompetent children, with no permanent skin or nail damage.