Case Number : Case 1560 - 17 June Posted By: Guest

Dermatomyositis did not crossed my mind (even if clinical description could fit) because this lichenoid reaction is extremely florid. I did think of lichenoid drug reaction because of some apoptotic keratinocytes that are far too high above the basal layer, no eosinophils though. Another differential that crossed my mind mainly because the patient is a young male was lichenoid syphilis as it can be a mimmicker both clinically and histologically. But I dont see plasma cells here. Third differential lichen planus actinicus (sometimes seen in young patients) but here the elbows are affected and there is not pigment incontinence (usually present in LPA). CPC is really important as Mona highlighted.

Agree with the differentials. Also thought about GVHD (in the right setting). Need clinical correlation. 

Agree with Mona: dermatomyositis is my first thought.

Agree with Gottron's papules: there is the typical lichenoid reaction pattern of dermatomyositis and fibrinoid/fibrous perivascular material in papillary dermis. DDx  with Acute Cutaneous Lupus.

after reading and learning more about gottron's papules I agree that it should be considered in the differential

This biopsy was taken from a knuckle. Additional clinical information: Ill-defined erythema on face below one eye. A number of knuckles with localised flat topped hyperkeratosis. Moderate periungual erythema affecting all finger nails (can be a sign of dermatomyositis). Scattered red papules on the elbows with some silvery scale looking like psoriasis. Rheumatology review: Pain in all 1st MCPJ's. Early morning stiffness. Wt. Loss. anorexia, nausea. o/e Marked synovitis of PIPJs & MCPJs and wrists. No proximal muscle weakness or tenderness. Obvious Gottron's papules, psoriasiform rash over elbows and possible heliotrope rash (unilateral). CK and ANA all normal. Virology screen negative.

Our report: Subtle interface inflammation with scattered necrotic keratinocytes in keeping with dermatomyositis.