Neuropathic pain is usually sharp or burning in character. With peripheral neuropathy, the pain and numbness usually occurs first in the feet. With more severe disease, it can progress up into the legs or involve the hands. Numbness in the feet can be especially dangerous as skin sores may unknowingly occur. If the sores become deep, or remain open, ulcers can develop. Weakness usually occurs first in the legs. If a trunk or root is involved, as in radiation-induced plexopathy or diabetic neuropathy, the thigh may become weak. If weakness begins in the periphery, as with environmental, chemotherapy, or compressive neuropathies, the foot may be affected first. In either instance, walking and climbing stairs can be difficult. Neuropathy can also affect the arm resulting in a weak grasp or shoulder function. When there is a loss of ability to do something, irrespective of the reason, it is called functional impairment.