Now you must be thinking, why have I given erythema nodosum along with Lichen scrofulosorum, whereas in previous explanation only Lichen scrofulosorum was given as the answer. Read below, there will be no confusion.Tuberculids can be classified into two groups:-1)   True (definite) tuberculids Mycobacterium tuberculosis plays a major etiological role. Examples:- Erythema induration (Bazin's disease), papulonecrotic tuberculid, Lichen scrofulosorum.2)   Facultative tuberculidsMycobacterium tuberculosis is one of the several etiological agents. Examples are:- Erythema nodosum.