An adult female neutered domestic shorthair cat of unknown age presented with a six-month history of progressive hind limb stiffness. Clinical examination revealed firm, painful enlargement of the quadriceps femoris muscles bilaterally, rigid extension of both hind limbs and restricted flexion of both stifle joints (Figure 1 (A)). There were no neurological deficits on examination. Doppler ultrasonography demonstrated normal arterial blood flow in the terminal aorta and iliac arteries. Radiography of the lumbar spine and hind limbs demonstrated multiple foci of mineralization in the quadriceps and hamstring muscles of both hind limbs (Figure 1 (B)).