The symptoms of DN are numbness, paresthesia (tingling), sensitivity to touch, pain, unsteadiness, and weakness. These symptoms are common to other polyneuropathies, but sensory symptoms are features of early DN. Painful symptoms occur commonly and include lancinating (electric shock-like, shooting), burning, freezing, cramping, and squeezing pain as typical descriptors. These symptoms affect the feet first, starting in the toes and soles of the feet, and then migrate proximally as the neuropathy progresses. The symptoms can be intermittent or persistent and are often most troublesome in the evenings when the patient is resting, or at night producing sleep disturbances. The only symptom of DN may be pain, or pain may accompany other symptoms of neuropathy. The painful symptoms range from mild to intolerable and can be accompanied by other features such as insomnia, impaired quality of life, inability to work, and low productivity in the home and at work [2]. The symptoms are most often chronic, lasting longer than 3 months and in many cases lasting for years. In treating patients, it is important to consider comorbidities that may be present (e.g.: depression) and tailor the treatment for the specific patient profile [4].

The physical examination may be normal despite the presence of characteristic painful symptoms indicating peripheral nerve injury. Other patients have sensory loss of the primary modalities of pinprick, temperature, light touch, vibration, and position sense, observed distally in the toes initially, and then more proximally in the lower limbs as the severity of neuropathy and degree of fiber loss increases. Finally, sensory loss will be evident in the upper limbs and also along the anterior chest as nerves of shorter length become affected. Early loss of pinprick, cold sensation, light touch, and vibration is often observed, but loss of position sense is a finding of late DN. Atrophy of small foot muscles, weakness, and loss of reflexes are similarly late signs. These physical findings are typical of both painful and painless DN.

These are common presentations of PDN. Some authorities have formulated scales to encompass the symptoms, such as the DN4 or Douleur neuropathique en 4 questions [5, 6]. These scales present simple tools for screening for the presence of PDN and may be useful. Bouhassira compared five simple screening tools for ­neuropathic pain [5] and found universal symptom descriptors across the scales for the presence of neuropathic pain, namely: burning pain, electric shock-like pain and pain evoked by touch, and tingling and numbness. In PDN, the symptoms of pain such as burning, electric shock-like, and aching coldness in the lower limbs occurring mainly at rest and at night, associated with tingling or numbness support the diagnosis [7]. Different scales that score the severity of pain have been developed including the Brief Pain Inventory (BPI) [8] and the Neuropathic Pain Questionnaire (NPQ) [9]. The NPQ provides a general assessment of neuropathic pain and aids in the discrimination of neuropathic from non-neuropathic pain states. This is a 12-item scale with 74.7% sensitivity and 77.6% specificity. A brief version consisting of three items can also indicate the presence of neuropathic pain [10]. The three items are tingling pain, numbness, and increased pain due to touch. The development of these scales is aimed at improving our ability to diagnose NP and can be used for the diagnosis of DPN. The severity of pain can be followed using the NPQ or the Neuropathic Pain Symptom Inventory (NPSI), a self-administered pain symptom questionnaire [11]. This pain questionnaire was developed initially to monitor the effects of therapy on neuropathic pain [12].

Despite this universal consensus, symptoms that are suggestive of neuropathic pain can be present in non-neuropathic pain disorders as shown in Table 3.2, so they are not specific and cannot be assumed to indicate the presence of DN when present [13]. Simple screening for the presence of DN can be accomplished by the use of the monofilament examination [14], although a normal test does not exclude a diagnosis of neuropathy. Other summary tools for DN include the Toronto Clinical Neuropathy Score that provides an assessment of severity, but not detailed information on painful symptoms [15].