Most of the syndromes listed here are likely to be a result of ischemia or infarction of nerves or nerve fascicles, because of a diabetic microvasculopathy. All but the first are special types of mononeuropathy multiplex. The polyneuropathy is associated with occlusion of small endoneurial blood vessels (vasonervorum) but possibly also incorporate a poorly understood metabolic abnormality; however, other theories of causation abound. In recent years, an inflammatory process has been postulated as yet another mechanism of peripheral nerve damage. These aspects are discussed further on.
The distal, symmetrical, primarily sensory form of polyneuropathy is the most common type. It is usually a chronic process, sometimes unnoticed by the patient. The main complaints are persistent and often distressing numbness and tingling, usually confined to the feet and lower legs and worse at night. The ankle jerks are absent and, sometimes, the patellar reflexes as well. As a rule, sensory loss is confined to the distal parts of the lower extremities, but in severe cases the hands are involved and the sensory loss may even spread to the anterior trunk, simulating a sensory level of spinal cord disease (Said et al, 1983). Trophic changes in the form of deep ulcerations and neuropathic degeneration of the joints (Charcot joints) are encountered in the most severe and long-standing cases, presumably as a result of sensory analgesia, trophic changes, and repetitive injury. (Foot ulcerations are more common simply as a result of the microvascular disease of skin in diabetic patients.) Muscle weakness is usually mild, but in some patients a distal sensory neuropathy is combined with a proximal weakness and wasting of the types mentioned earlier. Treatment of the acral pain may be a major problem and is discussed further on.
In another group of patients with diabetic polyneuropathy the clinical picture may be dominated instead by loss of deep sensation, ataxia, and atony of the bladder, with only slight weakness of the limbs, in which case it resembles tabes dorsalis (hence the term diabetic pseudotabes). The similarity to tabes dorsalis is even closer if lancinating pains in the legs, unreactive pupils, abdominal pains, and neuropathic arthropathy are present.
Among these, diabetic ophthalmoplegia is a common occurrence, usually in a patient with well-established diabetes. It commonly presents as isolated, painful third nerve palsy with sparing of pupillary function. In the first autopsied patient reported by Dreyfus and colleagues, there was an ischemic lesion in the center of the retroorbital portion of the third nerve. Subsequently, a similar case was described by Asbury and colleagues (1970). Slightly less often, the sixth nerve on one side is involved. The disorder was described in Chap. 13.
Isolated involvement of practically all the major peripheral nerves has been described in diabetes, but the ones most frequently affected are the femoral, sciatic, and peroneal nerves, in that order. Rarely is a nerve in the upper extremity affected. As mentioned, the acute mononeuropathies, both cranial and peripheral, are presumably a result of infarction of the nerve, but it is only in pathologic studies of the third nerve that this basis has been established. Recovery is the rule but may take many months.
This category overlaps with the mononeuropathies. A syndrome of painful unilateral or asymmetrical multiple neuropathies tends to occur in older patients with relatively mild or even unrecognized diabetes. Multiple nerves are affected in a random distribution (mononeuropathy multiplex). The mononeuropathies often emerge during periods of transition in the diabetic illness, for example, after an episode of hyperor hypoglycemia, when insulin treatment is initiated or adjusted, or when there has been rapid weight loss.