Diabetes in special situations: Insulin in diabetic foot ulcers

Disclosures

Introduction

Diabetes is ubiquitous in both medical and surgical settings, meaning that all medical professionals should be able to manage uncomplicated diabetes. However, in certain complicated clinical settings this is easier said than done. This opinion piece shares the basic principles of glycemic control in diabetic foot ulcers with both physicians and surgeons who manage this condition. Specifically, we discuss the role of insulin in management of diabetic foot ulcers.

Diabetic foot and diabetic foot infections are commonly encountered complications of diabetes [1]. Diabetic foot infections may be limb threatening or life threatening if not corrected in time. The principles of managing foot infections are simple and straightforward. Apart from wound care, antimicrobial therapy, and off-loading, the correction of metabolic abnormalities, including hyperglycemia, acidosis, azotemia, and electrolyte disturbances, is of utmost importance [2]. 

When is insulin recommended?

Recent guidance on the medical management of diabetic foot ulcers focuses only on antimicrobial therapy [3–5]. Comprehensive reviews suggest that existing oral antidiabetic drugs and insulin regimens must be intensified in diabetic foot infection, but do not offer detailed instructions on how to do this. Especially missing from current literature is clear-cut information on the indications for starting and intensifying insulin regimens in diabetic foot ulcers [6]. This is unfortunate, as evidence reveals that non-insulin using males have a higher risk of amputation than those who receive insulin while being treated for diabetic foot infection [7]. Recent studies have demonstrated the beneficial effects of systemic insulin therapy [8] and insulin pump therapy [9] on wound healing in diabetic foot. Pathophysiologic studies also support the use of insulin in infection [10].

Insulin triage

Here, we discuss the role of insulin in management of diabetic foot ulcers. While glycemic control is equally important in all persons with diabetes, including people with diabetic foot ulcers, the strategy and tools used may vary. With diabetic foot ulcers, the choice of glucose-lowering therapy depends upon the severity of infection.

The rubric used by the Infectious Diseases Society of America (IDSA) and the infection part of the perfusion, extent, depth, infection and sensation (PEDIS) classification of the International Working Group on the Diabetic Foot (IWGDF) can be utilized to suggest the appropriate choice of therapy [11, 12]. IWGDE/IDSA classify diabetic foot as being uninfected or infected. Infection is further classified as mild, moderate, or severe. Apart from evaluating the severity of the diabetic foot infection, the status of the affected limb (neurologic, vascular) and overall health status of the person (cognitive, metabolic, comorbidities) must be also assessed [6].

Insulin-naïve individuals

Neither IDSA or IWGDF suggest specific indications for insulin initiation. Based on pragmatic clinical sense, we suggest the following: Insulin-naïve individuals with poor overall health and evidence of metabolic decompensation must be initiated on insulin therapy, irrespective of severity of the foot ulcer (Fig. 1). Insulin-naïve individuals with limb-threatening vascular or neurologic compromise must also be started on insulin. Insulin-naïve individuals with moderate or severe infection (including osteomyelitis) must be initiated on insulin at presentation. Those with uninfected foot ulcer, or with mild infection (involving only skin or subcutaneous tissue; erythema <2 cm around the wound; no systemic symptoms or signs of infection), may be considered for insulin therapy in select situations (Box 1).

Figure 1. Insulin use in diabetic foot.

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Insulin users

Individuals already on insulin will need intensification of therapy if their overall health and metabolic status is poor. Intensification of therapy is defined as a change in insulin formulation, regimen, frequency or dosage, or addition of other therapeutic modalities, with a view to improving glycemic control [13].

The presence of azotemia or raised liver enzymes is an indication for insulin, especially if infection is present. Limb-threatening vascular or neurologic insufficiency of the affected limb is a clinical marker of the need for optimization or intensification of therapy, as is the presence of moderate or severe infection. Severely infected persons, or those who need hospitalization, must be switched to intensive subcutaneous or intravenous therapy. Persons with uninfected or mildly infected foot ulcers who are well controlled on their existing regimens may continue the same. Dosage may need to be increased or decreased, as there may be alterations in physical activity, dietary intake, and stress levels. These suggestions, though not mentioned in current guidelines, are a pragmatic and practical approach to diabetic foot ulcer care. 

Dynamic approach

Further requirement of insulin is linked to the course of the foot infection. Refractory ulcers, onset of systemic inflammation, and clinical worsening are indications to intensify insulin regimens and optimize insulin dosage. A stable foot ulcer, heading towards recovery, implies that the chosen glucose-lowering strategy is adequate. A fully healed ulcer, with no risk factors for recurrence, may allow de-escalation of insulin therapy and an eventual return to oral antidiabetic therapy.

Summary

Insulin is an important tool in the management of diabetic foot ulcers. We summarize our suggestions as below.

• In persons with a life-threatening or limb-threatening foot ulcer, insulin must be initiated or intensified to achieve rapid and sustained glycemic control.
• In persons with seemingly non-threatening ulcers and poor glycemic control, insulin must be initiated or intensified to achieve rapid and sustained glycemic control.
• In persons with seemingly non-threatening ulcers and adequate glycemic control, insulin may be considered in the presence of risk factors for recurrence, such as anatomical deformity or lymphedema.
• Guidelines for asymptomatic adults with diabetes may not be relevant to persons with diabetic foot injections.
• The choice of insulin regimens will depend upon various factors, including need for hospitalization, dietary pattern glucose profile, presence of comorbidities, and behavior of the foot ulcer.
• Insulin regimens which provide both fasting and postprandial control should be preferred.
• Insulin preparations which are associated with minimal hypoglycemia and glycemic variability should be preferred.