Nonfreezing Cold Injury

Nonfreezing cold injury is damage to the nerves, blood vessels and skin of the feet or hands after prolonged exposure to cold, wet conditions (about 0 to 15 degrees Celsius) without tissue freezing. It causes acute numbness and swelling and, in many, long term pain and cold sensitivity.

Exposure. Soldiers, outdoor and cold store workers, fishermen, mountaineers, and homeless people. Wet footwear, immobility, dependent limbs and tight boots increase the risk.

Epidemiology. Injury develops over hours to days of exposure. Prior injury increases the risk of recurrence and severity. Smoking and peripheral vascular disease add risk.

Stages. Pre-hyperaemic phase during and just after exposure: cold, numb, pale or mottled limbs with weak pulses. Hyperaemic phase over days to weeks: red, hot, swollen, painful limbs. Post-hyperaemic phase over weeks to years: cold sensitivity, pain, sweating, colour change and paraesthesia.

Outcome. Many patients have persistent cold hypersensitivity and neuropathic pain, and some cannot return to cold work.

Pathophysiology.

Prolonged cold and wet vasoconstriction produce ischaemia and endothelial injury, and rewarming causes reperfusion injury and vasodilation. Nerve injury affects small and large fibres, with Wallerian degeneration, so sensation is impaired and pain develops.

There is no ice crystal formation, which separates the injury from frostbite.

• Early: numb, cold, waxy or mottled skin with weak or absent pulses and impaired sensation.
• Hyperaemic phase: burning pain, throbbing, redness, swelling and blistering in some, with exquisite tenderness.
• Late: cold intolerance, paraesthesia, allodynia, sweating abnormalities, skin colour change and reduced dexterity or gait.

Red flags.

• Black, hard or non-blanching skin, or blisters with haemorrhage (tissue loss).
• Absent pulses, severe pain or spreading cellulitis and fever (infection).
• Rapid progression or symptoms beyond the extremities.

• Exposure history: duration, temperature, wetness, footwear and prior injuries.
• Clinical staging, skin temperature, capillary refill and pulses; Doppler ankle brachial pressure index.
• Quantitative sensory testing with thermal thresholds and, where available, skin biopsy for intraepidermal nerve fibre density; nerve conduction studies are often normal because small fibres are involved.
• Cold challenge testing and thermography in specialist centres.
• Exclude diabetes, vascular disease, connective tissue disease and vitamin deficiency.

Differential diagnosis. Frostbite, Raynaud phenomenon, peripheral arterial disease, diabetic and other small fibre neuropathy, erythromelalgia, chilblains (pernio), complex regional pain syndrome, vibration injury.

• Remove from cold and wet; take off wet boots and socks; air dry the feet gently, elevate, and rest at room temperature. Do not rub, massage or apply direct heat or hot water.
• Analgesia: paracetamol 1 g orally every 6 hours as needed, maximum 4 g in 24 hours (3 g if under 50 kg, chronic alcohol excess or liver disease), for the shortest period that controls pain. Reduce dose in hepatic impairment; extend dosing interval when eGFR is under 30.
• Neuropathic pain: pregabalin orally, 75 mg twice daily, increased after 3 to 7 days to 300 mg daily and, if needed after a further 7 days, to a maximum of 600 mg daily. Review at 4 weeks and stop if there is no meaningful benefit; withdraw over at least 1 week. Monitor sedation, dizziness, peripheral oedema, weight gain, mood and misuse. Adjust for renal function: creatinine clearance 30 to 60 mL/min, 75 to 300 mg daily in 2 or 3 divided doses; 15 to 30 mL/min, 25 to 150 mg daily; under 15 mL/min, 25 to 75 mg daily. Avoid in pregnancy unless benefit outweighs risk.
• Amitriptyline 10 mg orally at night, increased by 10 mg every 1 to 2 weeks as tolerated to 30 to 50 mg at night, maximum 75 mg at night. Review at 6 to 8 weeks and stop if there is no benefit. Monitor sedation, anticholinergic effects, postural hypotension and mood; baseline ECG when over 40 years or with cardiac risk. Avoid after recent myocardial infarction, with arrhythmia, in angle closure glaucoma or urinary retention, and with serotonergic drugs. Cap at 50 mg in older adults; reduce dose in hepatic impairment; no renal adjustment.
• Cold sensitivity or colour change: nifedipine modified release 30 mg orally once daily, increased after 2 weeks to 60 mg daily if needed. Usual maximum 60 mg daily. Monitor blood pressure, ankle oedema and headache. Reduce dose in hepatic impairment; no renal adjustment; avoid in pregnancy unless benefit outweighs risk. Evidence in this condition is limited.
• Stop smoking, keep the feet warm and dry, wear correctly fitted insulating boots, change damp socks, and avoid re-exposure to cold and wet for at least several weeks, with graded return directed by an occupational physician.
• Blisters: keep intact where possible, clean dressings, and treat infection by swab result and usual practice. Tetanus immunisation by status.

Monitoring. Review at 2 weeks, 6 weeks and 3 months; reassess function and pain at each visit and before return to cold work.

Referral and escalation. Vascular review for absent pulses or tissue loss; pain clinic or neurology for persistent neuropathic pain; occupational physician for fitness-for-cold-work assessment; notification and compensation where required.