Is Diabetic Sensory Neuropathy the Cause of Your Patient's Foot Pain?

By Dr. Mark Hinkes, DPM

After you've checked vital signs – pulse, respiration, blood pressure and temperature – don't forget what's considered to be the fifth vital sign: PAIN. For patients with diabetes, one of the most challenging health problems is foot pain. Diabetic sensory neuropathy is the most commonly associated reason for foot pain in the patient with diabetes. However, there can be multiple and even overlapping etiologies that should be identified and evaluated before jumping to a conclusion.

When confronted with sharp, burning, shooting, electric, tingling, stabbing pain or numbness in a patient with diabetes, diabetic sensory neuropathy is most often considered to be the culprit. However, before making that determination, the patient should have a thorough history with a focus on the foot, leg, and lumbar spine, combined with a foot examination and appropriate lab testing. It's important to remember that diabetic patients can have pain or sensory neuropathy that is NOT related to their diabetes. Identification of other possible causes of foot pain will assure that the patient gets the appropriate treatment that results in pain relief. The following outlines will help medical practitioners in performing a thorough foot health history, foot exam and laboratory testing and in identifying other causes of foot pain and neuropathy, including medications.

Determining the Cause of Foot Pain: Gather a Thorough Patient History

To determine the root cause of the patient's foot pain, a thorough history should uncover answers to the following questions:

• Onset and Duration of the Pain
• Previous Treatment and Results
• Time of Day the Pain Occurs
• Impact of Foot Gear on the Pain
• Review of Current Medications
• History of Foot or Leg Trauma
• History of Previous Foot or Leg Surgery
• History of Previous Vascular Surgery
• History of Back Surgery, Back Pain, or Radiculopathy
• Exposure to Toxins: Organophosphate Pesticides, Herbicides, Defoliants, Chemicals, Radiation
• Exposure to Heavy Metals: Gold Compounds, Lead, Arsenic, Mercury

Foot Exam Guidelines

The following is an outline for a foot exam for evaluating foot pain:
Remove shoes and socks from both feet as well as any dressings.

• Look at both feet for comparison
• Separate and look between the toes
• Examine the top and bottom of each foot and the back of each heel
• Identify osseous deformities
• Identify soft tissue deformities
• Identify nail deformities
• Identify ulcers
• Locate Foot Pain: Top, bottom, front, back, or sides
• Locate Area of Foot Affected: Front of foot, mid foot, rear foot, or entire foot
• Determine Quality of Pain: Burning, shooting, electric, tingling, cramping or numbness, dull, throbbing or achy
• Determine Pain Intensity at its Worst: 0 = no pain, 10 = worst pain
• Determine Nature of Pain: Constant vs. Episodic

The foot exam should address vascular, neurological and musculo-skeletal areas of the foot, including:

• Vascular: Dorsalis pedis pulse, posterior tibial pulse, digital capillary return, skin temperature knee to toe
• Neurological: Monofilament test, deep tendon reflexes, palpation of intermetatarsal spaces, percussion of tarsal tunnel
• Musculo-Skeletal: Joints range of motion; ankle, sub talar joint, 1st metatarsophalangeal joint, muscle power

The following is a brief review of lab tests for evaluating foot pain:

• X-Ray: foot, ankle, knee, pelvis, lumbar spine (In neuropathy, radiographic signs show demineralization, osteolysis)
• MRI: foot, ankle, lumbar spine (To rule out neuroma, tarsal tunnel syndrome, soft tissue tumor, fracture, Intervertebral disc abnormalities)
• Labs: HbA1c, CBC, Sedimentation Rate, CRP, ANA, Rheumatoid Factor, Uric Acid
• Vascular Testing: ABI, ABI with segmental pressures, duplex doppler, arteriogram

Common Causes of Foot Pain

The most common causes of foot pain include:

• Trauma: direct blunt, repetitive micro, overuse syndromes
• Shoe Gear: inappropriate or improperly-fitted shoes
• Environmental Conditions: lifestyle/activities
• Nerve Entrapment Syndromes: cutaneous nerve entrapments, intermetatarsal neuroma, neuritis, tarsal tunnel syndrome, compression neuropathy, lumbar radiculopathy
• Metabolic Diseases: gout, pseudo gout, infections, shingles (Post Herpetic Neuralgia)
• Vascular Diseases: ischemia, venous insufficiency, lymphangitis
• Musculo-skeletal Problems: arthritis, fractures, tumors, dislocations
• Inflammatory Soft Tissue: bursitis, capsulitis, fasciitis, myositis, tendonitis

Common Causes of Neuropathy

Causes of neuropathy, other than diabetes, that should be ruled out include:

• Autoimmune Diseases: lupus, rheumatoid arthritis, Guillain-Barre syndrome
• Cancer/ Chemotherapy
• Infectious Disease: Lyme disease
• Organ Failure: Liver, Kidney
• Pernicious Anemia
• Uremia
• Porphyria
• Vitamin Deficiencies
• Alcoholism
• Leprosy
• AIDS (whether from the disease or its treatment)
• Syphilis
• Inherited Disorders: amyloid polyneuropathy, Charcot-Marie-tooth disease

Medications, such as those listed below, can also cause neuropathy:

• Thiazide Diuretics
• Statin Drugs
• Colchicine
• Allopurinol
• Metronidazole (Flagyl)
• Isoniazid (Nydrazid, Laniazid)
• Taxol (a chemotherapeutic agent for ovarian and breast cancer)
• Amiodarone (an anti-arrhythmic drug)
• Vincristine (Oncovin, Vincasar) Cancer Drugs

While evaluating and managing foot pain in the patient with diabetes can be challenging, identifying the etiology of the pain will permit the prescribing of appropriate medication. When there is any doubt about the cause of a patient's foot pain, a referral to a Podiatrist with experience in treating patients with diabetes should be considered.

About the Author
Dr. Mark Hinkes is the former Chief of the Podiatry Service and Director of Podiatric Medical Education for the Veterans Affairs Medical Centers in Nashville and Murfreesboro, Tennessee, part of the Tennessee Valley Healthcare System. He was Chairman of the Preservation Amputation Care and Treatment (PACT) Program for more than a decade. He is Board Certified by the American Board of Foot and Ankle Surgery, and the American Professional Wound Care Association, and is a Fellow of the American College of Foot and Ankle Surgeons.

Dr. Hinkes spends time consulting, lecturing, and writing about foot health issues on his website, www.dr-mark.net. His most recent book, Healthy Feet for People with Diabetes, is a practical self-care guide designed for patient education.

The views and opinions expressed in this blog are solely those of the author, and do not represent the views of WoundSource, Kestrel Health Information, Inc., its affiliates, or subsidiary companies.