Dirty Hands

The 60-year-old black woman has a history of joint pain, muscle weakness, and Raynaud phenomenon. Why the “dirty hands”?

These are the hands of a 60-year-old black woman who, besides a chronic palmar discoloration, has a history of joint pain, muscle weakness, and Raynaud phenomenon. Physical examination showed proximal muscle weakness and mild synovitis in her metacarpophalangeal joints. She was mildly anemic, but renal function and urinalysis results were normal. Her creatine phosphokinase level was elevated at 3435 U/L. Her chest x-ray showed mild interstitial changes at the lung bases.

What best explains this patient’s “dirty hands”?