A female patient, 36 years, presented to me and my colleague, Dr Eman El-Nabarawy, with erythematous to hyperpigmented macules distributed mainly over her lower limbs with only few lesions over her upper limbs. The lesions showed a vaguely perceived reticulate or lividoid pattern over her legs. The lesions were asymptomatic and were present for 8 months. She has been treated with topical steroids with no improvement. The patient was referred to us for or biopsy taking and histopathological verification. On clinical basis, We were so confused and could not make up our minds.

The biopsy showed no specific features in the epidermis and the dermis, but down at the junction between the dermis and subcutaneous tissue, I found a large muscular vessel with a dense lymphocytic infiltrate around it and interestingly a ring of fibrinoid necrosis with neutrophils and dust was seen in the wall close to the lumen. The rest of small blood vessels in the subcutaneous fat showed nonspecific lymphohistiocytic infiltrate around them. I was perplexed!! Vasculitis in a large muscular vessel presenting as macules?? No palpable purpura, no nodules??? What is this???

I resorted to my text books trying to find an answer. This is a vasculitis in a large muscular vessel, so let's start by reading PAN (although not convinced at all clinically that this is PAN!!). And surprisingly I found it, macular arteritis (lymphocytic thrombophilic arteritis)!!! A latent, non nodule forming chronic variant of cutaneous polyarteritis nodosa that runs an indolent course. It presents with lymphocytic arteritis at various stages of evolution ranging from fibrinoid necrosis to endarteritis obliterans. Usually, there is no associated systemic manifestations. Although I have read this entity long time ago, I have never seen it and it did not cross my mind at all when I have seen the patient clinically, although this is how it presents typically!!Rare entities are usually forgotten in our daily practice. I was so happy and I felt lucky that I got this vessel in this section!!!

I did further readings and I came across an interesting article reporting 5 cases published in the Archives Of Dermatology in 2008*. Interestingly, 2 of the presented cases was exactly similar to my case. Although this entity usually does not show systemic manifestations or significant laboratory findings, one of the reported cases had antiphospholipid antibodies and one had a mutant factor V Leiden gene. Macular arteritis or lymphocytic thrombophilic arteritis should be kept in mind whenever we encounter hyperpigmented erythematous asymptomatic macular eruption with a lividoid pattern.

*Lymphocytic thrombophilic arteritis, See Lang et al., Archives of Dermatology. 2008;144(9):1175-1182