In 1889 he proved an early description of skin lesions associated with sarcoidosis, introducing the name "lupus pernio".

Lupus pernio is a chronic raised indurated (hardened) lesion of the skin, often purplish in color.

In contrast, patients with the disfiguring skin condition lupus pernio or cardiac or neurologic involvement rarely experience disease remission.

The most common lesions are erythema nodosum, plaques, maculopapular eruptions, subcutaneous nodules, and lupus pernio.

Among his numerous written works was a textbook on skin diseases titled Lehrbuch der hautkrankheiten, and three papers on lupus pernio.

The cutaneous symptoms vary, and range from rashes and noduli (small bumps) to erythema nodosum, granuloma annulare, or lupus pernio.

Recherches sur le lupus pernio et ses relations avec les sarcoides cutanées et sous-cutanées, (paper on Boeck's sarcoid).

Sur le lupus pernio, mémoire présenté en Novembre 1914 à la Société française de Dermatologie et de Syphiligraphie pour le Prix Zambaco, Stockholm 1934.