Discolorations of the skin anywhere on the body are a cause for concern for anyone but considering how significant legs are to our daily living, any pathology located around your legs seems to cause even more of a distress. There are a few different causes that could lead to purple or blue toes and they mostly depend on the age of the patient.
One of the first thoughts that a doctor will have when a patient presents with some type of skin discoloration is that there is a ischemic etiology to this disease. Emboli are able to easily log into the small vessels that make up your distal anatomy like toes and fingers leading to skin to become blood-starved. Coagulation diseases could lead to this type of phenomenon so if you are a younger patient with a new-found skin discoloration, make sure you go to your doctor and get a blood study done to determine if your condition could be caused by this irregularity. You can also see this type of damage after diseases like diabetes or peripheral artery disease where there is not enough blood reaching these highly sensitive areas.
Another possible reason that you will be suffering from skin discoloration is also related to the coagulation cascade. A side effect of blood-thinning medication could lead to skin color changes like purple toes. This medication goes by the name of warfarin and it is commonly used in patients who have had heart attacks, strokes or have coagulation problems. It is a medication designed to be used over the long-term so if you find that you are suffering from this side effect, notify your doctor immediately so an alternative medication can be administered instead.
If coagulation studies had been taken and there were still no irregularities, another possible cause that could be leading to purple toes could be an underlying connective tissue disorder. This is a condition that is normally seen in the pediatric population. They are very rare and are often not considered during the first or second round of diagnostic studies so if you have a child who has been to several specialists without finding a possible cause, this would be a good thing to consider. Connective tissue disorders are more likely to first present around the fingers and toes because of the delicate micro-capillaires that are found in this part of the body. When there is local inflammation, it will be more evident with redness and swelling in these small spaces.
The last possible condition that I will consider could be the damage due to the superficial skin leading to ischemia. This is very possible if you find yourself to be someone who enjoys winter activities like skiing. Not only are ski boots designed to be very constructive to help support your ankles, but being exposed to cold temperatures for a long period of time can lead to local hypothermia that can manifest as damage to the skin. This will lead to a purpling of the skin that can only get worse if you do not seek immediate medical attention.
There are still a number of various causes of purpling of the skin that you may be suffering from but the common denominator of all of these would be that you will need medical attention in order get to the bottom of the condition. It could just be due to abnormal anatomy of impaired venous flow, low blood pressures, or abnormal circulation but you need to act quickly in order to help preserve the limb. 
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