**3. Diabetic distal symmetric polyneuropathy in type 1 diabetes mellitus**

#### **3.1. Overview**

Distal Symmetric Polyneuropathy (DSP) is the most common type of neuropathy affecting patients with type 1 diabetes. Polyneuropathy is the greatest risk factor for non-traumatic amputations and confers a higher mortality risk [3, 4]. The incidence of DSP increases with duration of diabetes and with degree of hyperglycemia [5]. In type 1 diabetes, typically the incidence of DSP is linked to other microvascular complications of nephropathy and retinop‐ athy [6]. Unlike type 2 diabetes, polyneuropathy is rarely if ever present in the first five years of diagnosis. Metabolic memory in which improved metabolic control, even for a finite period, confers improved outcomes in the future is a phenomenon which was discovered with the Diabetes Complications and Control Treatment Trial, and may be an important factor to consider in the treatment of type 1 diabetic patients [7].

#### **3.2. Diagnostic criteria**

The case definition of typical DSP or diabetic sensorimotor polyneuropathy from the American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and the American Association of Physical Medicine and Rehabilitation is, "a combination of neuropathic symptoms, multiple signs, and abnormal electrodiagnostic studies" [8]. However, this does not distinguish typical DSP from atypical diabetic neuropa‐ thies [1]. A more precise definition for typical DSP proposed by neuromuscular experts at the 2011 Neurodiab Meeting suggested a tiered approach of possible, probable, confirmed and subclinical DSP. Possible DSP includes symptoms or signs of DSP such as decreased distal sensation or depressed ankle reflexes. Probable clinical DSP includes a combination of symptoms and signs of DSP. Confirmed DSP includes symptoms, signs, and abnormal nerve conduction study consistent with DSP (i.e. symmetric). Subclinical DSP would include patients with abnormal nerve conduction studies but no signs or symptoms of neuropathy [1]. Debate is ongoing as to whether abnormal skin biopsy with decreased epidermal nerve fiber density should be considered with nerve conduction study as a confirmatory test.
