Question:

A 44-year old driver complained of itchy eruption affecting his upper limbs for past 12 months. He enjoyed good past health and had taken no chronic medication or herbal remedies. The rash was itchy but did not affect his sleep. No family member was affected. He could not recall any special cause accounting for the itchy eruptions including insect bites or contact with chemicals. Blood tests screening for autoimmune diseases were all negative.

Answer: C. Lichen planus

Lichen planus remains an idiopathic skin disease. Pruritus is typically intense in this condition. The itchiness usually induces patients rubbing rather than scratching the skin for relief. Hence, excoriation marks are much less common than those in eczema and scabies. Lichen planus is characterized by shiny, flat papules and the colour is often described as violaceous. In many cases, the papules will last for a few months before they flatten gradually and become replaced by an area of pigmentation. The nails and the oral buccal mucosa should be examined to check for lesions of lichen planus affecting these sites. Mucous membrane lesions are common. White streaks, forming a lacework on the buccal mucosa or inner surface of the cheeks or gum margins are characteristic. The fingernails can be involved with changes of thinning of the nail plate. The adhesions form between the epidermis of dorsal nail fold and the nail bed leading to destruction of the nail and loss of the nail. Subungal hyperkeratosis and onycholysis may also be found. Characteristic histopathology findings including colloid bodies, pigmentary incontinence, orthokeratotic hyperkeratosis and band-like lymphohistiocytic infiltrate in the papillary dermis.

The major differential diagnosis will be lichenoid drug eruption which should be excluded by taking a detailed drug history. Excoriated marks, scaling, and polymorphic lesions in different stages of lesions (acute, subacute and chronic lesions) will be found in eczema. Burrows will be identified and severe nocturnal itchiness noted in normal people infested with Sarcoptes scabiei. Subacute lupus erythematosus should be excluded by a batch of screening immunological tests and if indicated by a histopathology section sent for direct immunofluorescent studies. Lupus erythematosus is also less common in a male.