What are the characteristic microscopic features of erythema nodosum?

The typical histologic features include a predominantly septal panniculitis with a slight spillover of inflammatory cells into the fat lobules. Cell types may include lymphocytes, neutrophils, and eosinophils, especially in acute disease. In older lesions, small granulomas (Miescher’s granulomas) are sometimes observed within connective tissue septa. Perivascular infiltrates are common, but true vasculitis with destruction of vessel walls is not observed.