(BMJ)—A 26-yo woman presented w/ rash on her abdomen and limbs x1y, plus R hand and L foot paresthesias x6mo. She had no fatigue, wt loss, fever, or arthralgia. Exam: palpable retiform erythema and broken livedo reticularis. Diminished sensation in R ulnar and L peroneal nerve distribution. Blood tests, incl full autoimmune screen, were WNL. What is the dx?
Thrombotic thrombocytopenic purpura
Cryoglobulinemia
Antiphospholipid syndrome
Systemic lupus erythematosus
Mononeuritis multiplex
You are correct. Mononeuritis multiplex is a peripheral neuropathy affecting 2 or more nerves and is commonly caused by vasculitis. Broken livedo reticularis is suggestive of cutaneous polyarteritis nodosa, a form of vasculitis assoc w/ mononeuritis multiplex. Cutaneous polyarteritis nodosa affects small- to medium-sized arteries but does not involve internal organs. Mononeuritis multiplex can be assoc w/ other forms of vasculitis, such as granulomatosis w/ polyangiitis and IgA vasculitis. CBC, glycated hemoglobin, hepatitis screen, antinuclear antibodies, extractable nuclear antigens, antineutrophil cytoplasmic antibodies, rheumatoid factor, and complement levels can help r/o other vasculitides, DM, connective tissue disorders, infections, and malignancy as possible causes of the mononeuritis multiplex. Skin bx can confirm the dx. This pt’s rash and paresthesias resolved w/ prednisolone and azathioprine.

BMJ 2017;359:j4109