Why might the arms and legs become red, cold, or swollen?

These symptoms are a manifestation and result of reduced motor activity in the affected extremities. The decreased temperature and changes in skin color (paleness, redness, or “marbling”) result from altered blood flow caused by paralysis (paresis) and muscle wasting (myopathy). With reduced motor activity, there is less of a “need” to supply blood to the limbs. The arteries supplying the limbs constrict (vasoconstriction) and “restrict” the blood flow.

This process is a normal occurrence that explains the development of redness and coldness. Swelling of the extremities is usually a sign of lymphedema, which is caused by an excessive accumulation of interstitial fluid. Lymphedema results from a discrepancy between the arterial blood supply to an extremity and a reduced venous outflow. Venous outflow depends largely on muscle tension (the venous-muscle pump), which in turn is reduced by muscle weakness and atrophy. Overall, the symptoms described—temperature, discoloration, and swelling—share a common and overlapping cause in altered vascular regulation.