Treatment induced neuropathy of diabetes (TIND), also referred to as insulin neuritis, is thought to be a rare iatrogenic cause of neuropathy that occurs in the setting of rapid glycemic control in individuals with a history of prolonged hyperglycemia.
In a recent paper, the investigators reported that a systematic review of all patients seen in a tertiary diabetic neuropathy referral center resulted in the diagnosis of TIND in \>10% of patients seen over a 5 year period of time. These individuals developed symptoms of neuropathy as a consequence of a sudden improvement in glycemic control. The neuropathy associated with TIND is a painful small fiber and autonomic neuropathy of acute onset, but is also associated with the simultaneous development of retinopathy and nephropathy.
TIND differs from the most prevalent generalized neuropathy of diabetes, the distal sensory-motor polyneuropathy, in several respects. The neuropathic pain has an acute onset, appearing within 8 weeks of glycemic change in contrast to the more insidious onset in the Diabetic sensorimotor polyneuropathy (DSP). The pain in TIND is more severe, and poorly responsive to interventions including opioids, whereas most patients with DSP respond to non-opioid interventions. Although the distribution of the pain is length dependent in individuals with TIND, it is frequently far more extensive than in DSP and the associated allodynia and hyperalgesia are much more prevalent. Autonomic symptoms and signs are common, prominent and appear acutely, in contrast to the relatively lower prevalence, gradual onset and slow progression in DSP. Finally, both the pain and autonomic features may be reversible in some patients.
The pathogenic mechanisms whereby this change in glucose results in nerve damage and/or dysfunction are not known. Proposed mechanisms include endoneurial ischemia due to epineurial arterio-venous shunts, apoptosis due to glucose deprivation, microvascular neuronal damage due to recurrent hypoglycemia and ectopic firing of regenerating axon sprouts, but these possibilities are unproven. A potential role for inflammation as a cause of TIND is supported by studies showing an increase in pro-inflammatory cytokines provoked by experimental hypoglycemia. This is reinforced by the association of hyperalgesia with prior exposure to hypoglycemia.
Other microvascular complications are commonly seen in patients with TIND. The simultaneous development of TIND, retinopathy and nephropathy in our cohort suggests a common systemic mechanism likely resulting in microvascular disease. Prior reports of 'early worsening retinopathy' associate a greater risk of retinopathy development with every percentage point decrease in the glycosylated hemoglobin, a result that parallels the neuropathy development in TIND. Furthermore, a link between hypoglycemia, production in pro-inflammatory cytokines, and the development of retinopathy has been proposed.
Treatment induced neuropathy is an iatrogenic cause of an acute, painful autonomic neuropathy in patients with poor glycemic control. Although the underlying mechanism is not yet known, there is a clear relationship between a rapid rate of glycemic control and the development of microvascular complications. Our preliminary data on upregulation of cytokines in individuals with TIND, and the similar findings noted in early worsening retinopathy, suggest the possibility that early intervention may improve outcomes.
The investigators have studied over 100 individuals with TIND in a longitudinal fashion. The characteristic disease progression is well described and related to the magnitude of the change in HbA1c. All patients develop severe neuropathic pain and progressive small fiber and autonomic neuropathy. The neuropathy progresses over 18-24 months and then may gradually improve.
The investigators have studied 4 patients with TIND that developed the acute onset of autonomic and peripheral neuropathy in the setting of rapid glycemic control. All 4 individuals had regular detailed neurological examinations, skin biopsy analysis of nerve fiber density, autonomic function testing and retinal examinations.
Within 4 weeks of the onset of neuropathic pain (within 8 weeks of the change in glucose levels), they were offered a trial of immune globulin administration at a dose of 2grams/kg divided into 5 doses of 0.4 grams/kg for 5 days. In 3 of 4 patients there was significant improvement in neuropathic pain (\>50%) and autonomic dysfunction with 4 weeks of immune globulin administration. In addition, there was a clinically significant increase in intra-epidermal nerve fiber density after 6 months (findings not seen in the large cohort of individuals that were untreated). One patient did not exhibit any clear improvement in neuropathic pain or autonomic dysfunction. Prior to immune globulin administration the investigators measured circulating cytokine levels in these 4 individuals. Those that responded tended to have higher circulating cytokine levels than that the individual that did not.
The investigators propose a prospective therapeutic study to determine the efficacy of IVIG in improving both neuropathic pain and nerve fiber structure and function in individuals with TIND. In addition, the investigators will attempt to define mechanisms that will predict success in this trial.
