ICD-10 Coding: Diabetic Foot Ulcer or Pressure Ulcer?

Even a podiatrist may not know for sure.

When is a diabetic’s foot ulcer a pressure ulcer? When is a pressure ulcer a diabetic foot ulcer? These are the questions we are going to explore in this two-part series of articles elicited by my disgruntlement with the advice in the third-quarter issue of Coding Clinic.

Shear and pressure are the mechanisms that lead to what are known as “pressure injuries.” In 2016, the National Pressure Ulcer Advisory Panel (NPUAP) recommended transitioning to the terminology of “pressure injury” because although underlying tissue may be damaged, overlying skin may appear intact. Pressure injuries with skin breakdown are considered pressure ulcers. An additional L89 code specifies the stage (depth of tissue injury) and the anatomical site.

Pressure ulcers form in sites that experience shear or pressure, typically in tissue overlying bony prominences such as elbows, the sacrum, hips, or heels. After sacral, heel ulcers are the second most common type of pressure injury. The etymology of the term “decubitus ulcer” is from the Latin, decumbere, which means “to lie down,” and thus it really relates to patients who are recumbent. “Pressure ulcer” or “injury” is more accurate, because the pathology may be noted in patients in other spatial positions, such as ischial tuberosity ulceration from prolonged sitting by a paraplegic. Ambulatory patients may develop pressure injury, but reduced mobility is a significant risk factor.

The term “non-pressure ulcer” was coined to designate a primary mechanism other than shear or pressure. If there is poor circulation, such as that caused by venous or arterial insufficiency or excessive moisture or trauma, a patient may develop a non-pressure ulcer. The word “chronic” is incorporated in the coding title, although chronicity is a measure of duration of time, not specific to a mechanism of injury. The ulceration of a pressure injury is often chronic as well.

There are medical diagnoses that predispose patients to develop secondary conditions. Diabetes mellitus is a pervasive endocrinopathy whereby hyperglycemia affects every organ and system in the body, including the nerves and blood vessels. It makes a patient more prone to infection and poor healing. Diabetics are prone to foot ulcers, often with contributions from neuropathic, ischemic, and most commonly, neuro-ischemic (both) etiologies.

Neuropathy occurs due to damage to the nerves and causes impaired sensation. After 10 years, ~90 percent of Type 1 and Type 2 diabetics have some degree of neuropathy, most commonly affecting the feet and legs, and 90 percent of diabetic foot ulcers have diabetic neuropathy as a contributing factor. If the diabetic doesn’t recognize discomfort due to nerve impairment, they may not adjust their shoes and socks or seek medical attention for minor cuts or blisters.

Diabetics also often have diseases of both large and small arteries. Poorly controlled blood sugars weaken the small blood vessel walls and predispose patients to arteriosclerosis. This impairs the circulation and causes ischemia of the soft tissues, especially of the lower extremities.

Many diabetics have both diabetic peripheral neuropathy and angiopathy. This makes them that much more likely to develop foot ulcers. A “diabetic foot ulcer,” which is caused exclusively by hyperglycemia, in the absence of neuropathy or ischemia, is a rarity. That term almost always refers to an ulcer on the foot of a diabetic that derives from neuro/ischemic etiology, as opposed to being strictly and principally due to pressure injury.

Heel ulcers, however, are usually a consequence of a pressure injury, although it is also possible to have another mechanism cause a non-pressure injury involving the heel. Diabetes may accelerate or complicate the injury.

Neuropathy results in malum perforans pedis (a.k.a. bad perforating foot) ulcers. These are painless, non-necrotic, circular lesions circumscribed by hyperkeratosis. They often overlie a metatarsal head. Ischemic wounds manifest local signs of ischemia such as thin, shiny, hairless skin with pallor and coldness. These are often found at areas of friction and may be painful.

Is it a pressure ulcer, a diabetic foot ulcer, or both? Is this a difference without a distinction? Is it just semantics, or is it clinically significant?

The American Orthopaedic Foot & Ankle Society states that “ulceration is an extremely common complication in diabetic patients (up to 12 percent of the population). The plantar surface is the most common site of ulceration, especially at areas of bony prominence.” The Society also points out that “the presence of neuropathy is the key factor in development of diabetic ulceration.”

The American Podiatric Medical Association adds that “(diabetic foot) ulcers form due to a combination of factors, such as lack of feeling in the foot, poor circulation, foot deformities, irritation (such as friction or pressure), and trauma, as well as duration of diabetes.” They go on to note that “vascular disease can complicate a foot ulcer, reducing the body’s ability to heal and increasing the risk for an infection.”

In the podiatric literature, NPUAP is often referenced as having given guidance to use “diabetic foot ulcer” for “any ulcer on the foot of a diabetic, even if arterial disease and/or pressure played a role in its development.” I think this is simplistic and derived from literature not aimed at physicians/APPs.

It is common in the literature to see the term “diabetic foot ulcer” used for all-comers. Why should we specifically carve out pressure ulcers? Pressure ulcers are deemed patient safety indicators and hospital acquired conditions because a concerted program for prevention and treatment can prevent them and protect our patients from iatrogenic harm. The diagnosis of a “pressure ulcer” may trigger prevalence and incident reporting.

Ultimately, the clinical concern is to treat the lesion appropriately, regardless of the name attached to it.

The treatment for both pressure ulcers and diabetic foot ulcers includes offloading (i.e., pressure mitigation, often by means of padding, shoe modifications, contact casts, boots, or non-weight-bearing strategies). Any non-healing wound should be assessed for neuropathy and perfusion status. Infection should be addressed, and wounds debrided as indicated. A multi-disciplinary approach, including wound care professionals, podiatry, and careful glucose management is prudent.

But you all surely want to know how to code this. You are going to have to wait for the second installment in this series for guidance on that. Until then, accept that there is sometimes clinical confusion as to whether the pathology indicates a diabetic foot ulcer or a pressure ulcer of the foot in a diabetic.

Program Note:

Listen to Dr. Remer every Tuesday on Talk Ten Tuesday, 10 a.m. ET.

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