As winter approaches, patients must be aware of the punishing effects of cold on the lower extremity. Given that patients with feet affected by the falling temperatures may present more commonly to podiatric offices, a correct diagnosis and treatment are vital.
Three patients presented with a single red, swollen, painful toe. I saw all patients individually but each had the same type of condition. For each patient, the condition had started several weeks before presentation with no obvious inciting cause. Each sought care from an internist, who placed the patients on antibiotics for a presumed toenail infection.
I saw all patients during the same week. There was no unusual past medical history with these patients. Further discussion revealed that the only similarity between them was that all had been outside at the presidential inauguration in cold temperatures. The temperature during the January event was 19ºF with a wind chill making it a frigid 6ºF.
It is very important that you really delve into the days before the occurrence of the foot problem. The fact that I was also at the inauguration was very helpful in making a diagnosis.
All three patients wore regular sneakers with regular cotton socks. None thought it would be that cold and that they would be standing still for that amount of time. Two of the patients were fair skinned and in their 20s. One patient was in her 60s and had a history of Raynaud’s disease. 
The three women had superficial frostbite. No laboratory test exists for frostbite as it is a clinical diagnosis.
Whether patients are outside exercising or are spectators at an outdoor event, they need to consider not only the air temperature but the wind chill factor as well. In the cold, patients are in jeopardy because the skin and the tissues below the skin’s surface are made up of cells that contain water. In freezing temperatures, the water in the cells can freeze and the cells can die. Frostbite is tissue damage caused by freezing.
Progressive symptoms of cold injuries include: initial coldness, stinging, burning and throbbing numbness followed by a complete loss of sensation. Other symptoms include: a loss of fine muscle dexterity (i.e., clumsiness of fingers); loss of large muscle dexterity (i.e., difficulty ambulating); and severe joint pain.
There are three types of frostbite: frostnip, superficial frostbite and deep frostbite.
Frostnip. Frostnip is a whitening of the tips of the fingertips and toes. It is slow to develop, is usually painless and seldom causes permanent tissue damage. Frostnip is not true frostbite, just super cold skin. It looks pale and feels cold. When the skin warms after frostnip, it may turn red. Underneath, the tissue is still warm and soft. 
The condition is not that serious and resolves by warming the foot/toe by moving and covering with extra layers of socks. It is also recommended that patients seek shelter and hold the toes between their hands to rewarm them until they appear normal again.
Superficial frostbite. The term for cold damaged tissue that has not frozen solid is superficial frostbite. When one pushes carefully on the cold skin, it is still pretty soft. It looks like frostnip but when you rewarm it (the same way you rewarm frostnip), fluid-filled blisters develop. The skin is hard and frozen, and looks white/blue. The tissue underneath the skin has not been affected yet.
As frostbite progresses or after the injured skin is warmed, the skin may be more pink or red than usual. The area will stay pink for several months although some people have permanent problems, such as pain, numbness and stiffness in the affected area.
Deep frostbite. In deep frostbite, the skin is numb and feels hard like wood. It looks pale or white. At this point, muscle and bone may be frozen. In more severe cases of frostbite, the skin can turn blue, gray or even black because of tissue injury. These changes sometimes do not happen until after the area warms up. Deep frostbite needs immediate medical attention. In severe cases, deep frostbite can lead to permanent injury, amputation and even death. 
Risk factors for frostbite include the following:
• inadequate shelter
• inadequate or constrictive clothing
• wind chill factor
• high altitude
• prolonged exposure to cold
• prolonged exposure to moisture
• malnutrition and exhaustion
• previous cold injury (previous injury increases risk twofold)
• peripheral vascular disease, diabetes mellitus or thyroid disease
• improper behavioral response to cold ambient temperature
• blocked arteries, atherosclerosis or other problems that affect blood circulation
• exposure to drugs with vasoconstrictive effects such as beta-blockers, which decrease the blood flow to the skin
• a low percentage of body fat
• drinking alcohol, which increases the loss of body heat
• drinking caffeine, which increases dehydration
• using nicotine, which decreases blood flow to limbs
Erysipelas. This is an acute infection of skin and subcutaneous tissue caused by beta-hemolytic Streptococcus with spreading inflammation and swelling. The area is warm and the patient may have a temperature.
Raynaud’s disease. This is a vasospastic disorder of the small peripheral arteries. The most common form is idiopathic primary Raynaud’s disease and is found in young women. Secondary Raynaud’s disease may be due to other connective or soft tissue disorders such as rheumatoid arthritis, systemic lupus or scleroderma. Occasionally, secondary Raynaud’s disease may be due to peripheral vascular occlusive disease, neurogenic lesions or drug intoxications.
Contributing factors include cold exposure and nicotine. Raynaud’s disease is often seasonal and most active in the cold weather months.
Paronychia. This infection develops along the edge of the toenail.
Thrombosis obliterans. This is inflammatory thrombosis of small and medium-sized arteries and some superficial veins, causing arterial ischemia in distal extremities and superficial thrombophlebitis. Tobacco use is the primary risk factor.
Dry gangrene. Dry gangrene is the term used to describe the death of tissue caused by a lack of blood supply. It is most common in people with advanced blockages of the arteries (arteriosclerosis) resulting from diabetes.
Acute irritant contact dermatitis. This occurs when the skin comes in contact with a strong toxic chemical and causes a rash (sharp borders with vesicles or bullae). The rash occurs within minutes to hours after exposure and, in most cases, healing occurs soon after exposure ceases.
Bullous diabeticorum. This is a distinct, spontaneous, noninflammatory, blistering condition of acral skin unique to patients with diabetes. Blisters occur spontaneously and abruptly, often overnight and usually without known antecedent trauma. Lesions tend to be asymptomatic although patients have described mild discomfort or burning. Blisters heal spontaneously within two to six weeks of onset.
With frostbite type injuries, two main reactions take place when tissues come into contact with very cold temperatures.
A vascular reaction occurs under the frozen superficial tissues and consists of damage to the wall of the blood vessels and leakage of plasma into the tissues (forming blisters). Red blood cells and platelets start to stick together, causing clots, ischemic damage and an increased viscosity of the remaining intravascular blood. The blood flow then stops via the action of the precapillary sphincters and the arteriovenous shunts open up and blood bypasses the frozen area. The diseased part is sacrificed for survival of the whole organism.
The second reaction is the freezing and crystallizing of fluids in the interstitial and cellular spaces due to prolonged exposure to freezing temperatures. The intracellular osmotic pressure rises and enzyme mechanisms are disturbed with subsequent cell death.
The toes contain multiple arteriovenous anastomoses that allow shunting of blood in order to preserve core temperature at the expense of peripheral tissue circulation. This leads to cold injuries.
The normal cutaneous flow is 200 to 250 mL/min. Maximal vasoconstriction occurs at 15°C (59ºF) with blood flow measured at 20 to 50 mL/min.
Below 15°C, vasoconstriction is interrupted by rhythmic bursts of vasodilation occurring three to five times per hour and lasting five to 10 minutes. At 10°C (50ºF), neurapraxia occurs and results in loss of cutaneous sensation. Below 0°C (32ºF), negligible cutaneous blood flow allows the skin to freeze.
Frostbite injury may be classified into a cascade and includes four phases: prefreeze, freeze, vascular stasis and late progressive ischemia. These all may overlap.
• The prefreeze phase consists of superficial tissue cooling.
• The freeze phase consists of ice crystal formation in the extracellular space more than the intracellular space.
• The vascular stasis phase consists of arteriovenous shunting at the margin between injured and uninjured tissue. This phase causes progressive microvasculature erythrocyte sludging, leading to stasis, coagulation and thrombus formation.
• The late progressive ischemia phase consists of thrombus-induced inflammation, hypoxia and anaerobic metabolism, leading to tissue necrosis.
The initial appearance of frostbite does not accurately predict the eventual extent and depth of tissue damage. Signs and symptoms vary according to severity of the frostbite injury. Frostbite is classified into four degrees of progressive injury identified by physical signs and the following sequelae.
A first-degree injury is characterized by epidermal involvement, which causes erythma, mild edema and subsequent desquamation and cold sensitivity.
A second-degree injury is full thickness skin freezing with substantial edema and formation of clear blisters. These blisters contract and dry within two to three weeks, forming a dark eschar.
A third-degree injury is characterized by the formation of hemorrhagic blisters, blue-grey discoloration of the skin, deep burning pain or rewarming, thick gangrene and eschar formation.
In a fourth-degree injury, muscle, bone and tendons are involved.
Long-term sequelae include the following:
• cold insensitivity;
• peeling skin;
• loss of fingernails or toenails;
• hyperhidrosis or anhidrosis;
• muscle atrophy;
• premature closure of epiphyses;
• decreased mineralization of bone; and
• joint stiffness.
A body part that suffers frostbite seldom recovers completely. Some degree of cold sensitivity and hyperhidrosis are common. Patients can experience neuropathies (including burning and tingling), decreased nail and hair growth, lymphedema, ulcerations and persistent Raynaud’s phenomenon in the affected part. Permanent tissue damage, such as subcutaneous tissue atrophy, bony defects on X-ray examination and abnormal epiphyseal growth, may occur. Patients should not smoke as this causes vasoconstriction and slows healing.
When it comes to frostnip, patients want to flex their feet and toes to help circulate blood in them. Sometimes movement is enough to reverse frostnip. It is also imperative to get out of the cold.
Remove wet clothing and tight items. Wet clothing greatly encourages the onset and worsening of frostbite. Patients should remove tight clothing, shoes and socks as they inhibit circulation. The outcome of a frostbite injury cannot be predicted in the first few days. For that reason, use the same treatment with all patients. Treatment involves re-warming the affected area at a temperature of 104° to 108°F (40° to 42°C). Treat the injury with aloe vera and splint, wrap and elevate the area.
One may give injections of tetanus vaccine and penicillin. These injections protect the patient against infection. One may also give an antiinflammatory drug, such as aspirin or ibuprofen. In some cases, narcotics may be necessary to treat the severe pain that occurs with deep frostbite.
If the frostbite is superficial, as was the case in my three patients, new pink skin will form underneath the discolored skin. The area will usually recover within six months although some people have permanent problems such as numbness, pain and stiffness in the affected area. In all patients, emphasize elevatation of the affected part to reduce swelling. Have patients drink warm, non-alcoholic, non-caffeinated fluids.
When severe (deep) frostbite occurs, anti-clotting drugs are recommended within 24 hours of injury and within 24 hours of re-warming. Blood clot-dissolving therapy helps reduce the injury caused when frozen skin is warmed again. Inflammation during thawing typically stimulates clotting that blocks small blood vessels, leading to cell death. Since the therapy reverses this clotting, this restores blood flow before permanent damage happens.
Dr. Morse is the President of the American Society of Podiatric Dermatology. He is a Fellow of the American College of Foot and Ankle Surgeons, and the American College of Foot and Ankle Orthopedics and Medicine. Dr. Morse is board certified in foot surgery.