A lichenoid drug eruption is a skin reaction to certain medications. The term “lichenoid” is used because the rash resembles the inflammatory skin condition lichen planus. This reaction is triggered by the body’s immune system responding to a specific drug and can appear after a delay, varying in severity.
Symptoms and Physical Presentation
The primary sign is the appearance of small, flat-topped bumps (papules) on the skin. These lesions are often shiny and can range in color from reddish-brown to a purplish hue. The papules may be covered with fine, white scales and can merge to form larger, scaly patches. The rash is accompanied by significant itching.
This eruption often presents symmetrically on the trunk and limbs. A notable characteristic is its tendency to appear in a photodistribution, meaning it is more prominent on sun-exposed skin.
The rash can be extensive, but blistering is an uncommon feature. Unlike classic lichen planus, the faint, lacy white lines known as Wickham’s striae are usually absent.
Common Causative Medications
A wide array of medications can provoke a lichenoid drug eruption, and the list grows as new drugs are developed. Antihypertensive drugs, used for high blood pressure, are a well-documented category. This group includes Angiotensin-Converting-Enzyme (ACE) inhibitors, beta-blockers, and thiazide diuretics.
Nonsteroidal anti-inflammatory drugs (NSAIDs), antimalarial medications, and certain antibiotics are also known to cause this reaction. Other triggers can include medications for high cholesterol, such as HMG-CoA reductase inhibitors, and proton-pump inhibitors used for acid reflux. Newer cancer therapies like checkpoint inhibitors are also recognized causes.
A defining feature is the significant delay between starting a medication and the rash’s appearance. This latent period can range from a few weeks to many months. In some instances, the rash develops even after the medication has been discontinued, making it challenging to pinpoint the specific trigger.
Diagnosis and Differentiation from Lichen Planus
Diagnosis begins with a comprehensive review of a patient’s medication history. A provider will create a timeline of all recently started medications, as the eruption can appear months after the first dose. This temporal relationship is a strong indicator, along with a physical examination of the rash.
A skin biopsy is often performed to confirm the diagnosis. The tissue sample shows a specific pattern of inflammation characteristic of a lichenoid process. The presence of certain inflammatory cells, like eosinophils, in the sample is more suggestive of a drug-induced reaction than idiopathic lichen planus.
Differentiating this eruption from idiopathic lichen planus is a key part of the process. The distribution pattern is a differentiator, as drug-induced eruptions are often widespread and favor sun-exposed areas. Classic lichen planus tends to appear on the flexor surfaces of the wrists and ankles.
Another feature is the absence of Wickham’s striae in drug-induced eruptions, which are common in idiopathic lichen planus. Involvement of the oral mucosa and nails is also common in lichen planus but rare in the drug-induced version.
Treatment and Resolution
The primary step in managing a lichenoid drug eruption is to identify and stop the medication causing the reaction. This must be done in consultation with a healthcare provider, who can determine a safe way to discontinue the drug and prescribe an alternative. If stopping the medication is not feasible, such as with certain cancer therapies, the rash is managed symptomatically.
To manage itching and inflammation, topical corticosteroids are frequently prescribed. These creams are applied directly to the affected skin to reduce the rash and provide relief. For widespread itching, oral antihistamines may also be recommended. In extensive cases, a course of oral corticosteroids like prednisone might be considered.
Once the offending drug is stopped, the rash begins to resolve, though this process can take several weeks to months. After the active rash clears, it is common for patches of skin discoloration, known as post-inflammatory hyperpigmentation, to remain. This discoloration is temporary and fades over time.