How would you diagnose this woman’s condition?

A 58-year-old female presented for evaluation of an itchy and tender rash of 3 months duration confined to 1 knee. This appeared shortly after she received a shot from her orthopedic physician (she believed it was a steroid shot), which helped her knee pain. She has been applying a steroid cream, which has not helped. She is otherwise healthy.

How would you diagnose this woman's condition?

A. Drug reaction to the injection into the knee
B. Bacterial infection from the injection with extension to the skin
C. Fungal infection from the injection with extension to the skin
D. Contact dermatitis to the steroid cream
E. Asteatotic eczema
F. Dermatophyte infection

(Answer and discussion on next page)

Answer: Tinea

A skin lesion potassium hydroxide exam (KOH) revealed a dermatophyte infection, which resolved uneventfully with a topical antifungal cream. Most likely it was exacerbated by the steroid injection in the knee and the probable knee brace or bandage that was worn until the injection took effect. A good knee/joint examination is necessary to ensure that the joint space is not involved (it was not). Since the steroid cream therapy was initiated after the onset of the rash, it only masked the typical appearance of the dermatophyte infection. Asteatotic eczema would typically not be asymmetrical unless the skin was different for each knee (it was not).