What is the cause of a pruritic, scaly rash on the posterior lateral base of both thumbs, present for approximately 2 months?

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Differential Diagnosis for Rash on Bilateral Hands

Single Most Likely Diagnosis

  • Dyshidrotic Eczema (Pompholyx): This condition is characterized by mildly pruritic, scaly, raised bumps on the hands and feet, often localized to the lateral aspects of the fingers and toes, or the palms and soles. The description and location of the rash, along with its chronic nature, make dyshidrotic eczema a strong candidate.

Other Likely Diagnoses

  • Contact Dermatitis: This could be either irritant or allergic in nature. Given the location on the hands, exposure to irritants or allergens is plausible, leading to a dermatitic reaction.
  • Psoriasis: While psoriasis can occur anywhere on the body, its appearance on the hands, particularly in areas subject to trauma or irritation, could present with scaly, raised bumps.
  • Tinea Manuum: A fungal infection of the hand, which could present with scaly, mildly pruritic lesions, although it typically involves the palmar surface.

Do Not Miss Diagnoses

  • Squamous Cell Carcinoma: Although rare, any persistent or changing skin lesion, especially in sun-exposed areas or areas of chronic irritation, warrants consideration of skin cancer. Early detection is crucial.
  • Lymphoma (Cutaneous T-Cell Lymphoma): Certain types of lymphoma can present with skin manifestations, including patches, plaques, or nodules. While rare, missing this diagnosis could have severe consequences.

Rare Diagnoses

  • Keratoacanthoma: A low-grade, or sometimes considered benign, tumor that can appear as a firm, round, skin-colored to red growth, often with a central crater. It's typically found on sun-exposed areas but can occur elsewhere.
  • Granuloma Annulare: A benign condition characterized by bumps arranged in a ring pattern, often on the hands or feet. It's less common and might not perfectly match the described distribution but could be considered in the differential.

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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