Plantar Abscess - an Unusual Initial Presentation of Diabetes Mellitus

Introduction

Diabetes mellitus is a chronic condition caused by either inadequate insulin production or by insulin resistance in the body, which leads to a long-term metabolic disorder. It is known to target approximately 537 million adults aged between 20-79 years globally. Further studies have predicted that by the year 2030, there will be 643 million people who will be affected.¹ India is known to be the epicentre of the global pandemic of diabetes mellitus. There is an increased prevalence seen mainly in the past four decades.² This is mainly due to an increase in development, demographic shifts, environmental factors, higher living standards, obesity, as well as the increased susceptibility observed in Indians due to genetic factors.³ The most commonly affected population in developing countries is aged between 45 and 64 years.⁴ Diabetes is a disease of individual cells, it is not just about hyperglycaemia and its complications – it causes multi-system involvement.

The most common diabetes-related cause for recurrent hospitalisation is foot wounds. Individuals with diabetes are known to have a tenfold increased risk of being hospitalised for soft tissue and bone infections of the foot compound to individuals without diabetes.⁵ The major microvascular complications seen are peripheral neuropathy, nephropathy, and retinopathy. Peripheral neuropathy is seen in almost 70% of patients with diabetes and may be one of the presenting features in certain cases, thus causing foot wounds and infections.⁶

Evidence suggests that hyperglycaemia can accelerate non-enzymatic glycosylation and collagen deposition in abnormal periarticular regions of the connective tissues, which causes alterations in the structural matrix and mechanical properties of the tissues. This results in widespread arthrofibrosis.⁷

Case Report

A 56-year-old male presented with a sudden onset, progressive left heel pain for two weeks, which was aggravated by walking. The pain gradually worsened during this period and was associated with redness, swelling, and blister formation over the plantar surface of the left foot. There was no known history of trauma or injury. He had a history of hypertension. He was afebrile, with a pulse rate of 112/min, respiratory rate of 18/min, blood pressure of 110/70 mmHg, and the peripheral oxygen saturation(SpO₂) of 98% on room air. Physical examination revealed localised tenderness over the calcaneum and the plantar aspect (sole) of the foot, with significant erythema and swelling. All his peripheral pulses were palpable, and sensory examination was normal.

Initial laboratory tests were suggestive of raised blood sugar level of 455 mg/dL and fasting blood sugar (FBS) of 174 mg/ dL. His C-reactive protein (CRP) CRP was elevated at 8.2 mg/L; haemoglobin was 12 g/dL, total leukocyte count (TLC) at 14,340/ μL, platelets of 284000/μL. Creatinine was 0.7 mg/dL, and electrolytes were 134/4.5/99. Urinalysis was normal.

The patient was initially started on broad-spectrum antibiotics (piperacillin-tazobactam and linezolid). Ultrasound imaging revealed a thickened plantar fascia with inflammatory changes and fat pad thickening. Magnetic resonance imaging (MRI) confirmed subcutaneous pus collection, but there was no evidence of osteomyelitis. A multiloculated T2 hyperintense and T1 slightly hyperintense lesion was seen in the abductor hallucis longus muscle, measuring 1.4 x 5.3 x 1.2 cm (transverse x anteroposterior x craniocaudal), with surrounding muscle oedema and thin peripheral enhancement. A similar curvilinear and lobulated T2 hyperintense subcutaneous signal was noted in the plantar aspect of the hind foot medially extending over 2.7 x 5.8 x 2.6 cm, without significant enhancement on postcontrast images. These findings were concerning for cellulitis, with an evolving abscess or, less likely, areas of necrosis (Figure 1-4).