From the Guidelines
Injecting lidocaine is not a reliable method to differentiate between lichenoid drug eruption and lichen planus. These two conditions are clinically and histologically similar, making distinction challenging. Instead, diagnosis relies on a thorough medication history, clinical examination, and sometimes skin biopsy. Lichenoid drug eruption is typically associated with medication use (common culprits include beta-blockers, thiazides, antimalarials, and NSAIDs) and resolves after discontinuation of the offending drug, while idiopathic lichen planus has no medication trigger. The distribution pattern can also help differentiate: lichenoid drug eruptions often have more widespread, asymmetric lesions, while lichen planus classically presents with symmetric, purple, polygonal, pruritic papules and plaques, often on flexor surfaces of wrists, forearms, and legs. Oral involvement is more common in lichen planus. If drug-induced disease is suspected, the recommended approach is to discontinue the potential causative medication and observe for improvement over weeks to months, rather than attempting lidocaine injection as a diagnostic test.
The provided evidence does not support the use of lidocaine injection as a diagnostic tool for differentiating between lichenoid drug eruption and lichen planus. The studies focus on the use of intravenous lidocaine for postoperative pain and recovery, and do not address its use in diagnosing skin conditions 1. The most recent and relevant guideline evidence suggests that high-potency topical steroids or tacrolimus are recommended for the treatment of lichen planus and lichenoid diseases, but does not mention lidocaine injection as a diagnostic or therapeutic option 1.
Key points to consider in differentiating between lichenoid drug eruption and lichen planus include:
- Medication history: Lichenoid drug eruption is often associated with medication use, while idiopathic lichen planus has no medication trigger.
- Clinical examination: Lichenoid drug eruptions often have more widespread, asymmetric lesions, while lichen planus classically presents with symmetric, purple, polygonal, pruritic papules and plaques.
- Distribution pattern: Lichen planus often affects flexor surfaces of wrists, forearms, and legs, while lichenoid drug eruptions can have a more widespread distribution.
- Oral involvement: Oral involvement is more common in lichen planus.
In summary, injecting lidocaine is not a recommended method for differentiating between lichenoid drug eruption and lichen planus, and diagnosis should rely on a thorough medication history, clinical examination, and sometimes skin biopsy, as supported by the most recent and relevant guideline evidence 1.
From the Research
Differentiation between Lichenoid Drug Eruption and Lichen Planus
- The differential diagnosis between lichenoid drug eruption (LDE) and lichen planus (LP) can be challenging due to similar clinical and histological signs 2.
- A study proposed a new diagnosis method for differentiating LDE from LP, which involves injecting 0.5 mL of 2% lidocaine solution into a papule, followed by histological examination 2.
- The formation of a blister (bulla) at the site of injection was considered a positive test result, and the study found that 18 out of 20 LDE patients developed a blister, while 12 out of 13 LP patients did not 2.
- The histological sections showed that the bulla corresponded to the separation of the epidermis from the dermis, suggesting that intracutaneous injection of lidocaine can be a sensitive and specific method to differentiate LDE from LP 2.
Comparison with Other Studies
- Other studies have focused on the treatment and diagnosis of oral lichen planus and oral lichenoid lesions, but do not provide direct evidence for the use of lidocaine injection in differentiating LDE from LP 3, 4, 5, 6.
- A study on histopathological discriminant criteria between LDE and idiopathic lichen planus found that certain histopathological signs, such as focal parakeratosis and cytoid bodies, can suggest a drug etiology, but do not provide a pathognomonic differential diagnosis 5.
- Another study reported a case of lichenoid drug eruption associated with sildenafil citratus, highlighting the importance of a detailed anamnestic history in making the correct differential diagnosis between LDE and LP 4.