A 49 y.o. male presents with a pruritic rash on the top of his head and his penis.

What would be in the differential?

Our patient had lichen planus. The term lichen planus was derived from the Greek word leichen meaning tree moss and the Latin word planus meaning flat.  It was first used by Wilson in 1869.  This is a skin disease caused by a cell-mediated response of unknown origin. It may be found in diseases of altered immunity , such as ulcerative colitis, vitiligo, dermatomyositis, myasthenia gravis and hepatitis C. It can be caused by medications including diuretics, ACE inhibitors, beta-blockers and NSAIDs.  It is also associated with syphilis which is what our patient had.

Wickham's striae, white lacy lines on the oral mucosa.

Lichen planus affects one percent of the general population .  It causes scaly raised areas that may occur on the genitals, skin or in the mouth where classically it forms Wichkham’s striae.  It can cause ridged nails and is most common  in patients in their 30s to 50s.  The lesions are intensely pruritic. The differential in this case with penile and scalp lesions  would have included lichen planus, psoriasis or lichen sclerosus.  Lichen sclerosus presents with a hypopigmented glans with a cellophane-like texture and phimosis. 

lichen sclerosus

Pathologically, there is degeneration of the basal layer of the epidermis and a bandlike lymphocytic infiltrate obscuring the dermal epidermal junction. There is irregular epidermal hyperplasia with  a saw tooth appearance.  The basal layer of skin shows necrosis with keratinocyte damage.The pathology is what distinguishes it from an ID reaction where fungal infections in the feet can cause a diffuse eczematous rash. 

It is treated with topical corticosteroids and may last up to a year. Our patient was treated for syphilis and given steroids for his scalp.  His phone number has changed and he has been lost to follow up.

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Young SK, Kim MH, Kim CW, et al. A case of palmoplantar lichen planus mimicking secondary syphilis. Ann Dermatol 2009 21(4): 429-431.

Singh JP, Priyadarshi V, Goel H, Vijay M, et al.  Penile lichen sclerosus: a n urologist’s nightmare! A singlecenter experience. Urol Ann 2015 7(3): 303-308.

Wilson E. On lichen planus. J Cutan Med Dis Skin.  1869;3:117-132.