Id Reaction

Basics

Description

A generalized skin reaction associated with various infectious and inflammatory cutaneous conditions distant from the main rash of the disease:

  • Id is a word termination often combined with a root reflecting the causative factor (ie, bacterid, syphilid, and tuberculid). The dermatophytid is the most frequently referenced id reaction in dermatology. A dermatophytid is an autosensitization reaction in which a secondary cutaneous reaction occurs at a site distant to a primary fungal infection. The eruption begins typically within 1–2 weeks of the onset of the main lesion or following exacerbation of the main lesion.
  • System(s) affected: Skin/Exocrine
  • Synonym(s): Dermatophytid, trichophytid, autoeczematization

Epidemiology

  • Predominant age: All ages
  • Predominant sex: Male = Female

Incidence

Unknown; no good data source

Prevalence

Common

Risk Factors

  • Fungal infection of the skin
  • Stasis dermatitis

General Prevention

  • Minimize factors for developing fungal infections.
  • Promptly treat any developing fungal infection.

Etiology

Precise pathophysiology is uncertain. Circulating antigens may react with antibodies at sensitized areas of the skin, or abnormal immune recognition of autologous skin antigens may occur.

Commonly Associated Conditions

  • Primary fungal infection
  • Stasis dermatitis

Id is a word termination often combined with a root reflecting the causative factor (ie, bacterid, syphilid, and tuberculid). The dermatophytid is the most frequently referenced id reaction in dermatology. A dermatophytid is an autosensitization reaction in which a secondary cutaneous reaction occurs at a site distant to a primary fungal infection. The eruption begins typically within 1–2 weeks of the onset of the main lesion or following exacerbation of the main lesion.

Diagnosis

History

Itchy rash: Assess for the primary fungal or bacterial lesions that would have preceded the onset of the id reaction by days to weeks.

Physical Exam

  • Common:
    • Symmetric, pruritic vesicles on the hands
    • Tinea infection on the feet; contact or other eczematous dermatosis; or bacterial, fungal, or viral infection of the skin
    • Generalized reactions can occur.
  • Less common:
    • Papules
    • Lichenoid eruption
  • Eczematoid eruption

Diagnostic Tests & Interpretation

Lab

  • Fungal infection at the primary site proven by potassium hydroxide (KOH) or fungal culture
  • No fungal elements demonstrable at the site of the presumed id reaction
  • Special tests: Skin shows a positive trichophyton reaction.

Follow-Up & Special Considerations

The id reaction resolves with successful eradication of the primary skin condition.

Pathological Findings

  • Vesicles in the upper dermis
  • Superficial perivascular lymphohistiocytic infiltrate
  • Small numbers of eosinophils
  • Moderate acanthosis
  • Increased granular cell layer
  • No infectious agents present in biopsy specimen

Differential Diagnosis

  • Pompholyx (dyshidrotic eczema)
  • Contact dermatitis
  • Drug eruptions
  • Pustular psoriasis
  • Folliculitis
  • Scabies

Treatment

Medication

First Line

  • Antihistamines for any pruritus
  • Topical steroids for pruritus
  • Systemic steroids only if reaction is severe or generalized
  • Contraindications: Refer to manufacturer’s profile of each drug.
  • Precautions: Refer to manufacturer’s profile of each drug.
  • Significant possible interactions: Refer to manufacturer’s profile of each drug.

Second Line

  • Topical and/or systemic antifungals for identified associated fungal infection (common)
  • Topical or systemic antibiotics for any secondary infection

Additional Treatment

General Measures

  • Appropriate health care: Outpatient
  • Treatment of the underlying infection or eczematous dermatitis
  • Symptomatic treatment of pruritus with antihistamines and/or topical steroids if needed (may require class 1 or 2 steroid)
  • Treatment for secondary bacterial infection

Ongoing Care

Patient Education

Avoid hot, humid conditions that promote fungal growth. Aerate susceptible body areas (eg, wear sandals or open footwear). If possible, wear boxer shorts or loose-fitting clothing, dry off wet skin after bathing, and use powders and antiperspirants to make the environment less conducive to fungal growth. Treat primary dermatitis promptly.

Prognosis

After appropriate treatment, complete resolution in a few days to 2 weeks

Complications

Secondary bacterial infection (cellulitis)

Additional Reading

1. Habif T. Clinical Dermatology, 4th ed. St. Louis: Mosby, 2004.

Codes

ICD9

  • 110.9 Dermatophytosis of unspecified site
  • 692.89 Contact dermatitis and other eczema due to other specified agents

Snomed

  • 3014005 Id reaction (disorder)
  • 30668009 allergy-sensitivity to fungi syndrome (disorder)

Clinical Pearls

This is a diagnosis in the category of “If you don’t think of it, you won’t think of it,” so when you see one skin lesion follow another, think of the id reaction.

About the author

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