Scrofuloderma is a rare skin manifestation of tuberculosis (TB) due to a skin invasion of Mycobacterium tuberculosis from spread of TB from nearby lymph nodes, bone or joints, frequently associated with pulmonary TB.
It is characterised by firm, painless, subcutaneous, slowly growing nodules that ulcerate. They can form fistulae that chronically drain serious, purulent or caseous discharge.
Mantoux (or other TB skin tests) are positive. Biopsy is diagnostic.
Treatment is with anti-tubercular drugs.