Dear Dr. Hibberd:
I have had panniculitis in my leg for five years and my doctor seems to have no idea what is causing it. Can you explain what this condition is and how to treat it?

Answer: Panniculitis refers to a group of conditions that involve inflammation of the fat under the skin. Despite having very different causes, most forms of panniculitis look alike, are irregular, and under the skin. Cold injury to fat tissue can also result in a type of panniculitis, called cold panniculitis. It can also be due to abrupt withdrawal of high dose of steroids. Severe panniculitis can result from the deficiency alpha1-antitrypsin inhibitor, a form of inherited disorder. Since your lesion is in your leg, it is likely to be an idiopathic nodular panniculitis, also known as Weber-Christian disease, which has no known cause. You could also have associated fever, malaise, arthralgia, and myalgia.
The diagnosis is established by a skin biopsy as there are characteristic microscopic features depending on the cause. Have you had a skin biopsy done? You might want to discuss this with your doctor at the next visit.