Case Number : Case 656 - 13 Dec Posted By: Guest

Mixed lobular and septal panniculitis due to vasculitis. I would favor polyarteritis nodosa for correlation with serology.

PAN vs erythema induratum of Bazin

PAN

Agree with Dr. Saeb DD, however I would prefer erythema induratum of Bazin.

PAN

Favor Erythema Induratum of Basin (nodular vasculitis).

I think it’s a case of classic polyarteritis nodosa. There’s a leukocytoclastic vasculitis of small and medium-sized arteries of the subcutaneous fat. Typically, damaged vessels are in different stages of development. Early lesion (right bottom) shows fibrinoid necrosis of the arterial wall with a mixed infiltrate rich in neutrophilic nuclear dust present within and around the arterial wall. Late lesion (left bottom) is evidenced by perivascular fibrosis and occlusion of the vessel lumen by myxoid fibro-intimal proliferation.
As the resulting panniculitis seems to be restricted to the vicinity of the involved vessels and granulomas couldn’t be found, I suppose less likely the diagnosis of erythema induratum / nodular vasculitis.

The inflammation seems to be mixed but predominantly septal. I do not think vasculitis in any way rules out Erythema nodosum, which would be my favoured diagnosis in this case given the clinical. However I have found it difficult to distinguish this from vasculitis seen in PAN and haven't yet seen a convincing explanation to differentiate the two. Would be grateful of Prof. McKee can maybe explain the differentiating features.

PAN...nice images of neutrophilic vasculitis of musc. vessels with occlusion

The clinical history is of major importance. A female with tender nodules on the calves is characteristic of nodular vasculitis (erythema induratum). In erythema nodosum, the lesions are on the shins. There is a mixed septal and lobular panniculitis with both acute and chronic inflammation. Granulomata are not evident but this may be a result of the small size of the biopsy specimen and they may have been present elsewhere in the lesion (not biopsied). I think that PAN is a very good differential diagnosis but clinically, I doubt very much that lesions would have been limited to the calves. Obviously laboratory investigations would have been necesary to make a diagnosis of PAN. I have no information as the case was shared with me as an example of classical nodular vascuilitis. I think that vasculitis is always a difficult diagnostic differential as the features are not specific and overlap many conditions. Often a full clincial and laboratory workup are necessary before a definitive diagnosis can be made.