Case Study: A 62-Year-Old Man With “Brittle” Type 1 Diabetes

Presentation K.A. is a 62-year-old man with a 42year history of “brittle” type 1 diabetes. When first seen at our office, he complained of erratic and unpredictable blood glucose levels despite adhering to a rigid multiple daily insulin injection protocol. He was taking four insulin injections per day (NPH before breakfast and at bedtime and lispro insulin (Humalog) before each meal) and performing self-monitoring of blood glucose (SMBG) eight times daily, including preand postprandially and whenever he felt symptomatic. K.A. injected his morning NPH in the abdomen, his lunch and dinner insulin in the arms, and his bedtime NPH in the buttocks. He was sedentary and did not exercise. He had been counting carbohydrates to adjust his insulin for only 5 months. Five years ago, K.A. developed frequent severe hypoglycemia, during which he lost consciousness and presented in the hospital emergency room. His blood glucose levels had been <30 mg/dl on each of his eight emergency room visits. In the ensuing 5 years, he had developed hypoglycemic unawareness. Because of the frequency of hypoglycemic events with altered levels of consciousness (at least 30 episodes documented per month) the patient’s driver’s license was revoked, and he sought an early retirement from his job as an electrical engineer. He believed that his control might improve if he were placed on an insulin pump. K.A. is 71 inches tall and weighs 74 kg. His blood pressure at our initial visit was 124/86 mmHg without orthostatic changes. His diabetes-related complications included autoimmune hypothyroidism, microalbuminuria, peripheral sensory neuropathy, and nocturnal diarrhea. His HbA1c was 7.3%, and his fasting capillary blood glucose was 125 mg/dl. His liver function was normal, but he did have proteinuria (245 mg/dl in a 24-h urine collection). His creatinine was 1.2 mg/dl. His thyroid and adrenal function studies were normal. After unsuccessful attempts to finetune his insulin injections based on carbohydrate counting and preprandial glucose readings, we placed him on continuous subcutaneous insulin infusion (CSII) therapy. Unfortunately, K.A. did not experience any improvement in his glycemic control. He became more depressed and frustrated because he was still experiencing daily hypoglycemic events. After 2 weeks of insulin pump therapy, he was placed on a continuous glucose monitoring system (CGMS). Figure 1 shows the results of his CGMS test. Analysis of the sensor readings demonstrated that the patient’s SMBG records were not consistent with those obtained by interstitial fluid sensing. At 8:00 a.m., the patient’s meter (circle markers in Figure 1) read 298 mg/dl, but the sensor reading (dark line in Figure 1) was 118 mg/dl. When he believed that his blood glucose was high based on erroneous meter readings, he would give himself a compensatory bolus of insulin via his pump. There was no consistent correlation between the sensor and the meter. Thus, K.A. was constantly administering insulin based on inaccurate SMBG readings. The disparity between the sensor and the meter was so substantial that the sensor would stop functioning and have to be re-calibrated by the patient throughout the day. (See Figure 2.) This indicated a problem with the meter, rather than a malfunctioning of the CGMS. When the patient was informed about the inaccuracy of his meter, he explained that he had purchased the device, which used test strips, 10 years ago and he had never doubted its accuracy. Although reluctant to part from his favorite meter, the patient’s diabetes control improved when he was provided with a more accurate device. Two months after receiving his new meter,