The diagnosis is based on physical examination. First of all, inspection can reveal atrophy of intraosseous muscles in the hands and feet, a sign of denervation. When muscle atrophy in the feet is extensive, deformity of the foot architecture can occur, characterized by high foot arch, metatarsal head protrusion, and a shift of the subcutaneous fat normally present under the metatarsal heads towards the bases of the toes, resulting in claw-toe deformity. When autonomic neuropathy coexists, which happens frequently, the foot is reddish, superficial veins are prominent and on palpation it is warm and dry due to lack of sweating. Presence of calluses on pressure sites on the soles is an indication that excessively high pressures are exercised at these sites.
Further examination usually reveals symmetric sensory loss (of touch, pain, temperature and vibration), which starts from the peripheral parts of the extremities and extends centrally (stocking-glove sensory loss distribution). Lower extremity involvement usually precedes the upper extremity involvement. Loss of one type of sensation can be detected at one site (for example, of temperature discrimination), while at the same time another type of sensation (for example, pain) can be normal. Sensory loss can also be segmental, such as complete loss of sensation at one site of the foot and intact sensation at a neighbouring site. Furthermore, the sensory deficient area is not abruptly demarcated from the normal one, but a hypoaesthesia zone usually lies in between. The Achilles tendon reflexes are usually absent and in more advanced disease even knee reflexes can be absent. Deep sensory loss is quite common, with patients reporting imbalance and frequent episodes of falls and trauma.
Special tests (nerve conduction velocity and quantitative examinations of nerve function) are not necessary for the diagnosis in routine clinical practice. A study in the USA found that around 10 percent of diabetics had peripheral neuropathy due to another cause, other than DM.
Table 15.1. Causes of peripheral neuropathy
Toxic substances Neoplasms
Autonomic diseases Genetic
Vitamin B12 or B6
Guillain Barre syndrome
Chronic inflammatory demyelinating polyneuropathy Vasculitides (polyarteritis nodosa) Charcot-Marie-Tooth disease
Consequently, before neuropathy can be attributed to DM, other causes need to be ruled out. These causes of peripheral neuropathy are described in Table 15.1.
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