scrofuloderma

Result from break of skin overlying a tuberculous focus,usually at a lymph node but also at the skin over infected bones or joints.

Historically a high prevalence was found in children infected with m.bovis .

The oral or tonsillar primary lesion progresses to cervical adenitis, formation of cold abscesses and secondary breakdown of the overlying skin.

Tubercle bacilli can be isolated from purulent discharge.

Tuberculin sensitivity is usually marked. 

Spontaneous healing can occur but often takes years. Lupus vulgaris may develop in the vicinity of healing scrofuloderma.

Metastatic tuberculous abscesses is a variant of scrofuloderma that occurs following hematogenous  spread of mycobacteria to skin in tuberculin sensitive individuals.

Typically occurs in malnourished children or severely immunosupressed patients.