Differential Diagnosis for Lichenoid Drug Rash

Single Most Likely Diagnosis

• Lichen planus: This is a chronic inflammatory condition that can present with lichenoid lesions, and it is often difficult to distinguish from a lichenoid drug rash based on clinical appearance alone. The presence of polygonal, flat-topped papules and Wickham's striae can support this diagnosis.

Other Likely Diagnoses

• Contact dermatitis: Irritant or allergic contact dermatitis can sometimes present with lichenoid features, especially if the reaction is chronic. A thorough history of exposures and patch testing can help differentiate this from a drug-induced rash.
• Graft-versus-host disease (GVHD): In patients who have undergone bone marrow or stem cell transplantation, GVHD can manifest with lichenoid skin lesions. The clinical context and history of transplantation are key to considering this diagnosis.
• Chronic actinic dermatitis: This condition, also known as photosensitive eczema, can present with lichenoid features, particularly in sun-exposed areas. Photopatch testing may be helpful in diagnosis.

Do Not Miss Diagnoses

• Pemphigus foliaceus: Although this autoimmune blistering disease typically presents with flaccid blisters, in some cases, it can manifest with lichenoid lesions. Missing this diagnosis could lead to severe consequences due to the potential for widespread blistering and skin loss.
• Bullous pemphigoid: Another autoimmune blistering disease, bullous pemphigoid can occasionally present with lichenoid features before the development of characteristic blisters. Early recognition is crucial to prevent extensive skin involvement.
• Cutaneous T-cell lymphoma (CTCL): Mycosis fungoides, a type of CTCL, can present with lichenoid patches or plaques, among other skin manifestations. Given the potential for progression to more aggressive disease, it is critical not to miss this diagnosis.

Rare Diagnoses

• Lichenoid keratosis: A rare, benign condition that can present as a solitary lichenoid papule. It is often considered a variant of lichen planus but can be distinguished by its solitary nature and different histological features.
• Keratosis lichenoides chronica: A very rare condition characterized by lichenoid papules and plaques, often in a linear or reticulated pattern, accompanied by palmoplantar keratoderma. Its rarity and distinctive clinical features make it a diagnosis to consider when common causes have been ruled out.