Foot temperature in healthy individuals: effects of ambient temperature and age.

BACKGROUND: Patient complaints of excessively warm or cold feet are common in medical practice. Such symptoms can be caused by underlying vascular or neurologic disease, and measurement of foot temperature during daily activity and sleep could provide a deeper understanding of their actual thermal basis. METHODS: We used a Thermochron iButton to assess surface foot temperature variation and its relationship to ambient temperature during the day with activity and at night during sleep in 39 healthy individuals aged 18 to 65 years in a temperate region of the United States. We simultaneously used actigraphy to record leg movement. RESULTS: We identified a mean +/- SD awake temperature of 30.6 degrees +/- 2.6 degrees C and asleep temperature of 34.0 degrees +/- 1.8 degrees C, with values reaching as low as 15.9 degrees C in the winter and as high as 37.5 degrees C in the summer. Foot temperature was found to be independent of foot movement or sex; however, there was, as expected, a strong association between foot temperature and ambient temperature (r = .59, P < .001). Several measures of foot temperature variation demonstrated a significant or near-significant reduction with increasing age, including the Euclidean distance (r = -.38, P = .02) for awake periods and the variance (r = -.30, P = .06) during sleep. CONCLUSIONS: These results provide data on the normal variation of foot temperature in individuals living in a temperate climate and demonstrate the potential use of Thermochron iButton technology in clinical contexts, including the evaluation of patients with excessively warm or cold feet.

Clinical utility of electrodiagnostic studies in the inpatient setting.

Although nerve conduction studies/electromyograms are often requested to evaluate hospitalized patients (inpatients) with suspected neuromuscular diseases, their clinical utility has not been studied. They can be technically challenging, especially in intensive care units. We studied the contribution of inpatient electromyograms (IP-EMGs) to the management of patients with suspected neuromuscular disorders. A total of 103 IP-EMGs in 98 patients were analyzed. IP-EMGs confirmed the clinical diagnosis in 53.3% and provided a new, clinically relevant diagnosis in 12.6%. IP-EMGs revealed only an incidental diagnosis in 14.5%, were inconclusive in 16.5%, and were normal in 3%. In over a quarter of patients, IP-EMGs assisted in planning further diagnostic evaluation or treatment. Although IP-EMGs most often only confirm already suspected diagnoses, in a substantial minority of patients they lead to the identification of clinically unsuspected, significant diagnoses that alter subsequent clinical care. Muscle Nerve 40: 195-199, 2009.

Effect of newly proposed CK reference limits on neuromuscular diagnosis.

The objective was to determine the effect of a proposed increase in the upper reference limits of serum creatine kinase (CK) on neuromuscular disease diagnosis. This was a retrospective study of 94 Caucasian subjects (49 women and 45 men) in whom a neuromuscular physician ordered a CK as part of their evaluation. The patients were divided into two groups: those with diagnoses that either should or could elevate serum CK, and those with diagnoses that should not elevate serum CK. Sensitivities and specificities of the manufacturer's and the newly proposed upper reference limits were determined. For women, raising the upper reference limit of CK from 140 IU/L to 201 IU/L reduced the sensitivity of the test from 50% to 29%, while increasing the specificity from 67% to 80%. For men, raising the upper reference limit of CK from 174 IU/L to 322 IU/L reduced the sensitivity from 80% to 60%, while increasing the specificity from 63% to 80%. The newly proposed upper reference limits resulted in a false-negative CK of clinical significance in 7 of 94 subjects. Increasing the upper reference limit for CK reduced the sensitivity and increased the specificity of serum CK for neuromuscular disease diagnosis. Such a change will reduce unnecessary referrals and invasive diagnostic testing in patients with asymptomatic CK elevations. The clinical impact of the loss in sensitivity is small. If these new upper reference limits are adopted, neuromuscular physicians should be aware that a normal CK level does not exclude a diagnosis of myopathy.

Impaired distal thermoregulation in diabetes and diabetic polyneuropathy.

OBJECTIVE: To determine how thermoregulation of the feet is affected by diabetes and diabetic polyneuropathy in both wakefulness and sleep. RESEARCH DESIGN AND METHODS: Normal subjects, diabetic subjects without neuropathy, diabetic subjects with small-fiber diabetic polyneuropathy, and those with advanced diabetic polyneuropathy were categorized based on neurological examination, nerve conduction studies, and quantitative sensory testing. Subjects underwent foot temperature monitoring using an iButton device attached to the foot and a second iButton for recording of ambient temperature. Socks and footwear were standardized, and subjects maintained an activity diary. Data were collected over a 32-h period and analyzed. RESULTS: A total of 39 normal subjects, 28 patients with diabetes but without diabetic polyneuropathy, 14 patients with isolated small-fiber diabetic polyneuropathy, and 27 patients with more advanced diabetic polyneuropathy participated. No consistent differences in foot temperature regulation between the four groups were identified during wakefulness. During sleep, however, multiple metrics revealed significant abnormalities in the diabetic patients. These included reduced mean foot temperature (P < 0.001), reduced maximal temperature (P < 0.001), increased rate of cooling (P < 0.001), as well as increased frequency of variation (P = 0.005), supporting that patients with diabetic polyneuropathy and even those with only diabetes but no diabetic polyneuropathy have impaired nocturnal thermoregulation. CONCLUSIONS: Nocturnal foot thermoregulation is impaired in patients with diabetes and diabetic polyneuropathy. Because neurons are highly temperature sensitive and because foot warming is part of the normal biology of sleep onset and maintenance, these findings suggest new potentially treatable mechanisms of diabetes-associated nocturnal pain and sleep disturbance.

A methodology for the real-time measurement of distal extremity temperature.

The real-time measurement of distal extremity temperature may have a wide variety of uses, from assessing occupational cold exposure to determining the impact of autonomic dysfunction on normal thermoregulation. In this study, we describe a novel approach to the measurement of this physiologic parameter by the use of datalogger iButtons affixed to the foot and outer clothing, the latter serving as an approximate measure of ambient temperature, in conjunction with the measurement of foot movement via actigraphy. This approach was piloted in 20 individuals, all of whom were also requested to maintain a diary of activities during the measurement period. The technique was found to be reliable and well tolerated amongst the group of subjects, with no individual suffering an adverse reaction (e.g. skin breakdown) while wearing the device. However, periods of ambient temperature data were suspect in at least 25% of the recordings, presumably due to misplacement of the sensor. Several approaches to data analysis suggested themselves, including separate analysis of the nocturnal/sleep and awake data sets. The use of datalogger iButtons in conjunction with actigraphy appears to be a potential useful approach for the acquisition of real-time distal extremity temperature and movement data and has the potential of serving a variety of clinical and research purposes.

Vitamin B(12) and methylmalonic acid levels in patients presenting with polyneuropathy.

This study was designed to determine the prevalence of definite vitamin B(12) deficiency (defined as < or =240 pg/ml) and possible vitamin B(12) deficiency (defined as >240 pg/ml and a methylmalonic acid [MMA] level >243 nmol/L) in patients with polyneuropathy and to determine whether patients in both groups respond to vitamin B(12) repletion. We performed a retrospective cohort study of 581 patients presenting with polyneuropathy over a 2-year period; 4% had definite vitamin B(12) deficiency and 32% had possible deficiency as the sole or contributing cause for their polyneuropathy. For those who received treatment with vitamin B(12), subjective improvement was seen in 87% with definite and in 43% with possible deficiency. Possible vitamin B(12) deficiency, defined as an elevated MMA level, is a common finding in patients with polyneuropathy and treatment of these patients with vitamin B(12) may lead to clinical improvement.

Sural and radial sensory responses in healthy adults: diagnostic implications for polyneuropathy.

We prospectively performed sural and radial sensory nerve conduction studies in 92 healthy subjects, aged between 21 and 88 years, both to determine the lower limits of normal (LLN) and to assess the effects of age and body mass index (BMI) on the sural and radial sensory nerve action potential (SNAP) amplitudes and on the sural/radial amplitude ratio (SRAR). Using the nonparametric bootstrap method to calculate 95% confidence intervals, we found that the 5% LLN values for sural and radial SNAPs were 14 microV and 25.5 microV in subjects aged < or =39 years, 7 microV and 17.4 microV in subjects aged 40-59 years, and 3 microV and 12 microV in subjects aged > or =60 years. The 5% LLN for SRAR for all patients was 0.21. Sural and radial SNAP amplitudes but not SRAR were strongly and inversely correlated with age and BMI. These age-adjusted normal values and revised SRAR will aid in the electrodiagnosis of polyneuropathy.

Ulnar neuropathy in the forearm: A possible complication of diabetes mellitus.

Ulnar neuropathy in the forearm is an unusual cause of hand weakness and sensory loss that is most often attributed to compression of the nerve distally within the humero-ulnar arcade (cubital tunnel). An association with diabetes mellitus, however, has not been reported. We identified four patients with type I diabetes mellitus and clinical findings suggestive of ulnar neuropathy in whom electrophysiologic testing revealed partial conduction block or abnormal temporal dispersion within the forearm segment of the ulnar nerve. Although evidence for a mild underlying polyneuropathy was present in three patients, the ulnar nerve abnormalities were disproportionately severe. In all cases, a Martin-Grüber anastomosis was excluded. Whether this lesion is due to an increased propensity to focal compression of the ulnar nerve within the humero-ulnar arcade or whether it represents a localized manifestation of the generalized polyneuropathy remains to be determined.

Evaluation and treatment of low back pain: an evidence-based approach to clinical care.

Low back pain is a common reason for patient visits to a health care provider. For most patients, low back symptoms are nonspecific, meaning that the pain is localized to the back or buttocks and is due to a presumed musculoligamentous process. For patients with radicular leg symptoms, a precise etiology is more commonly identified. The history and physical examination usually provide clues to the uncommon but potentially serious causes of low back pain, as well as to those patients at risk for prolonged recovery. Diagnostic testing should not be a routine part of the initial evaluation, but used selectively based upon the history, examination, and initial treatment response. For patients without significant neurological impairment, initial treatments should include activity modification, nonnarcotic analgesics, and education. For patients whose symptoms are not improving over 2 to 4 weeks, referral for physical treatments is appropriate. A variety of therapeutic options of limited or unproven benefit are available for patients with radicular leg symptoms or chronic low back pain. Patients with radicular pain and little or no neurological findings should receive conservative treatment, but elective surgery is appropriate for those with nerve root compression who are unresponsive to conservative therapy.

Diagnostic accuracy of electrodiagnostic testing in the evaluation of weakness.

Electrodiagnostic testing is often used in the evaluation of patients presenting with weakness, but the diagnostic accuracy of the test in this setting is unknown. We prospectively identified 100 patients presenting to our electromyography (EMG) laboratory with the chief complaint of weakness, and compared their referring diagnosis with the electrophysiological diagnosis reached after electrodiagnostic testing. We reviewed each patient's medical record 9 months after EMG to yield a final diagnosis. Electrodiagnostic testing led to a single diagnosis in 79% of the cases; in 31%, this diagnosis was unsuspected by the referring clinician. Adequate follow-up was available for 79% of the patients. The electrodiagnostic testing resulted in a single, correct diagnosis in 73% of the patients and provided more than one possible diagnosis, one of which was correct, in an additional 18%, for an overall diagnostic accuracy of 91% in this group of patients presenting with weakness.