Diabetes mellitus is a disease with high blood glucose levels causing problems with the bodys ability to produce or use insulin. Statistics show that 25.8 million people suffer from diabetes in the United States. Diabetes is classified into two types: Type 1 and Type 2 diabetes mellitus. (Diabetes Basics, 2012)
Type 1 diabetes mellitus was formerly known as juvenile diabetes. It is most commonly diagnosed in children and young adults. Diabetes is classified as Type 1 when the body does not produce insulin. Insulin is a hormone found in the body. It changes sugars, starches, and foods into energy. Type 1 diabetes only accounts for 5% of people. Due to therapy and treatments people with Type 1 diabetes can live long and healthy lives. (Diabetes Basics, 2012)
Diabetes is classified as Type 2 when the body does not make enough insulin or the cells reject insulin. The body must have insulin to use glucose for energy. Your body takes the foods you eat and changes them to glucose. Glucose is the energy for the cells in the body. When the body does not have enough insulin or rejects the insulin, glucose cannot be used. Due to this, it builds up and causes diabetic complications. (Diabetes Basics, 2012)
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There are many symptoms associated with diabetes. Some of these symptoms include frequent urination, fatigue, and thirst, however, they may not happen at all. Other symptoms could be nerve damage to the hands and feet resulting in tingling and numbness, recurring bladder infections, and vaginal yeast infections. Symptoms of high blood sugar or hyperglycemia would include blurry vision, excessive thirst, frequent urination, weight loss, hunger, and tiredness. (President and Fellows of Harvard College, 2009)
Common test for diagnosing diabetes mellitus include: random plasma glucose test, fasting plasma glucose test, and glycohemoglobin test. The random plasma glucose test looks at the levels of glucose in the blood. You have a high probability of having diabetes if your glucose level goes beyond 200 mg/dL. This test is not as reliable as the fasting plasma glucose test, due to the fact that what you eat affects results of your test. (President and Fellows of Harvard College, 2009)
When taking the Fasting plasma glucose test one must cease from eating for at least eight hours. This will limit the chance of meals skewing the results. A normal fasting plasma glucose level is less than 100 mg/dL. Fasting plasma glucose levels equal to or greater than 126 mg/dL indicates diabetes. It is common to run the test twice to confirm results. (President and Fellows of Harvard College, 2009)
Glycohemoglobin test , or HbA1c, is a newer test that is looked to become the future standard for diagnosing diabetes. The HbA1c looks at an average blood sugar level of the previous two to three months. People without diabetes have an HbA1c level of around 5%. An HbA1c of 5% means that 5% of hemoglobin molecules have glucose connected to them. High blood sugar levels will increase the percent of HbA1c. It has been shown that having low HbA1c levels decreases chances of diabetic complications. (President and Fellows of Harvard College, 2009).
"Diabetic peripheral neuropathy (DPN) is one of the most common and debilitating complications of diabetes mellitus (Wu, 2011)." "Diabetic neuropathy affects the sensory, autonomic, and motor neurons of the peripheral nervous system (Duby et al., 2004)." There are several risk factors for developing diabetic neuropathy. The main risk factor is poor glycemic control or hyperglycemia which leads into poor metabolic control (Duby et al., 2004). Also, cardiovascular risk factors play an important role such as age, sex, hypertension, high cholesterol, obesity, and sedentary lifestyle (Duby et al., 2004). Signs and symptoms include, but are not limited to the following; allodynia, burning, hyperesthesia, and paresthesia (Wu, 2011). At first, signs and symptoms may be intermittent, but gradually worsen overtime (Wu, 2011). Eventually, this will interfere with daily routines or activities of daily living (ADLs) and social life (Wu, 2011). A sedentary lifestyle will lead to an increase risk of falls and other possible co-morbidities (i.e., hip fracture) (Kruse, 2010). Sensorimotor or distal symmetrical polyneuropathy is the most common form of diabetic neuropathy (Schaper et al., 2009). Distal symmetrical polyneuropathy affects both small and large sensory nerve fibers of the peripheral neverous system (Duby et al., 2004). Small sensory nerve fibers are responsible for conducting nociceptive stimuli, touch, and warmth sensation (Duby et al., 2004). Large sensory nerve fibers transmit proprioception, cold, and vibration sensation (Duby et al., 2004). Distal symmetrical polyneuropathy begins in the distal extremities and moves proximally (Duby et al., 2004). The loss of innervation leads to muscle wasting and foot deformities causing calluses and ulceration (Duby et al., 2004). Distal symmetrical polyneuropathy is the primary risk factor for developing a diabetic foot ulcer, which is responsible for 85% of lower-extremity amputations (Duby et al., 2004).
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Even though distal symmetrical polyneuropathy is the most common form of diabetic neuropathy, autonomic neuropathy should be recognized as a growing form of diabetic neuropathy (Duby et al., 2004). There are several forms of autonomic neuropathy which affect the autonomic nervous system (Duby et al., 2004). A few common forms of autonomic neuropathy include cardiovascular, gastrointestinal, and genitourinary autonomic neuropathies all of which produce an array of co morbidities (Duby et al., 2004). During a 10-year period, cardiovascular autonomic neuropathy (CAN) increases morbidity and mortality rates among type 1 and type 2 diabetes by 22 percentage points higher when compared with diabetes patients without CAN (Duby et al., 2004). Since CAN affect both the sympathetic and parasympathetic nervous systems, this will lead to exercise intolerance, orthostatic hypotension, and myocardial infarction (Duby et al., 2004). Gastrointestinal autonomic neuropathy can affect the entire GI system, but gastroparesis is the most common complication (Duby et al., 2004). Gastroparesis affects gastric emptying which may result in bloating, cramping, heartburn, and/or nausea and vomiting (Duby et al., 2004). Also, gastroparesis may interfere with the absorption of glucose or antidiabetic medication (Duby et al., 2004). Gastrointestinal autonomic neuropathy may result in gastroesophageal reflux disease (GERD), fecal incontinence, diarrhea, and severe constipation (Duby et al., 2004). Gentiourinary autonomic neuropathy affects both female and male urinary and sexual functions (Duby et al., 2004). Both sexes may experience bladder enlargement, urinary retention, and urinary incontinence (Duby et al., 2004). Women may suffer from increased vaginal dryness and painful intercourse (Duby et al., 2004). Men may suffer from erectile dysfunction and impotence (Duby et al., 2004).
Sensory systems receive information from the environment through receptors at the periphery of the body and transmit this information to the central nervous system. There the information is used for three main functions: sensations, control of movement, and maintaining arousal. Sensation is a conscious experience, even though not all sensory information is perceived (Kandel, Schwartz, & Jessel, *ROYS BOOK*& 1991). All sensations arising from skin, connective tissues, voluntary muscles, periosteum, teeth, and so forth belong to the general somatic sensory system, commonly referred to as the somatosensory system. The general senses include light touch or tactile discrimination and sensations of pressure or deep touch, vibration, proprioception, pain, and temperature. The somatosensory pathway consists of three neurons: the first neuron is in the sensory ganglia, the second is in the spinal cord or brainstem or both, and the third is in the thalamus (Young & Tolbert). There are three steps to sensory reception: (a) a stimulus occurs, (b) events in which the stimulus is converted into a message of nerve impulses, and (c) a response to this message, often in the perception or conscious experience of sensations. Sensory systems facilitate four qualities of a stimulus that can be connected quantitatively with a sensation: modality, intensity, duration, and location (K,S, &J, 1991). Stimulus information is represented in a series of action potentials by a process of neural encoding. When the amplitude of the receptor potential reaches the threshold of the cell's trigger zone, an action potential is generated. The lowest stimulus intensity that evokes a sensation is called the absolute, or detection threshold (Greenspan & LaMotte, 1993).
The somatosensory system is unique in that its receptors are distributed throughout the body and process many kinds of stimuli. The other sensory systems are localized to one area of the body and process only one kind of stimulus (Martin & Jessell, 1991). For example, the visual system is localized to the head and only processes light into visual perception. The modalities processed by the somatosensory system include touch, proprioception, pain, and temperature. Touch is elicited by mechanical stimulation of the body surface. Proprioception is elicited by mechanical displacements of the muscles and joints. Pain is elicited by noxious (tissue damaging) stimuli. The thermal modality is elicited by cool and warm stimuli. There are submodalities as well. For example, touch can include superficial touch and deep touch (pressure).
There are five specialized receptors in human that detect different stimuli. Those receptors are chemoreceptors, mechanoreceptors, thermoreceptors, photoreceptors, and nocioceptors (Martin, 1991). Nociceptors signal painful or noxious stimuli. Mechanical nociceptors, associated with fast pain, are free nerve endings activated by sharp or pinprick type stimuli. Their firing rate increases proportionate to the intensity of the potentially destructive stimulus, and the signal is propagated rapidly to the CNS by myelinated (AÎ´) afferents. Thermal nociceptors signal noxious heart or cold temperatures. Polymodal nociceptors respond to any destructive mechanical, thermal, or chemical stimuli resulting from tissue damage and are the underlying basis for the sensation of slow, burning type of pain.
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Cold, cool, warm, and hot sensations below and above normal skin temperature are sensed by thermoreceptors. Cold receptors fire most vigorously about 10Â°C below normal skin temperature whereas warmth receptors signal at their highest frequency 10Â°C above normal skin temperature. Warmth receptors are not activated by temperatures above 50Â°C. Temperatures at 50Â°C or higher are perceived as pain.
Tactile stimulation activated encapsulated mechanoreceptors by stretching the receptor membrane and opening ionic channels, leading to the receptor's depolarization and the resultant generation of action potentials in the primary afferent axons. Five different mechanoreceptors differ morphologically by their structure and location in the skin, and physiologically by the relative sizes of their receptive fields and most importantly by the types of functional information they encode.
Discrete tactile stimulation is detected by Merkel discs and Meissner corpuscles located in the superficial layers predominately in glabrous skin. Merkel discs have the smallest receptive fields, signal discrete indentations of the skin, and provide information about the curvature of objects. Meissner corpuscles are responsive to abrupt changes in the shape and edges of objects or irregularities on the surface of objects. In hairy skin sensory axons are incorporated into the hair follicle. Displacements of adjacent hairs activate different hair follicle receptors, providing additional information to the brain about discrete stimulation. Pacinian corpuscles and Ruffini endings are buried in the subcutaneous tissue and sense displacements of wide areas of the skin.
The skin on the foot is a combination of hairy and glabrous. On the dorsum of the foot, the skin is thin and mobile with sparse hair and there is little subcutaneous fat. The skin of the plantar surface of the foot is thin on the toes and instep but thick over the heel and ball of the foot. The plantar foot skin contains many sweat glands and a large amount of subcutaneous fat. Skin of the plantar foot is bound to the underlying structures by fibrous connective tissue and is thus relatively immobile (Moore, 1992).
Summary of Sensation
The action potentials created by receptors are transmitted over a distance to the central nervous system. Receptor neurons converge onto second order neurons and then third and higher neurons (Shumway-Cook & Woollacoot, 2007).
Different types of sensation are carried in parallel pathways in the CNS. For example, information on cutaneous, muscle, tendon, and joint sensibility are carried up to the somatosensory cortex and other higher brain centers by the dorsal column-medial lemniscal system. The Anterolateral system transmits information on crude touch and pressure, and thus contributes in a minor way to touch and limb proprioception. It also plays a major role in relaying information related to thermal and nociception to higher brain centers (SC & W, 2007).
Information from all these ascending somatosensory tracts goes through the thalamus. In addition, the thalamus receives information from a number of other areas of the brain, including the basal ganglia and the cerebellum. Thus the thalamus is a major processing center of the brain.
The protocols for measuring tactile functioning involves administering several different stimuli in blinded fashion and asking respondents to identify each one from a list of possible alternatives. It is assumed that the ability to identify the stimulus correctly reflects the respondent's underlying level of function in that particular sensory domain (Schumm et al, 2009).
The somatosensory examination rarely reveals absolute anesthesia because of the considerable overlap of the terminal fields of the primary afferent axons in the dorsal axon of the spinal cord. What a patient feels is a change in the perception of the stimulus as it passes from a normally innervated area to one that has been denervated. This change in perception is especially obvious if the lesion involves a spinal root. Therefore, it is important to ask the patient to compare the sensations presented at two areas, either by stimulating the two extremities in turn or by crossing dermatomes on a single extremity (Kingsley, 2000).
Many people have sensory deficits derived from alterations at the receptor level. Mild deficits occur as a result of aging, or they may occur due to skin disorders, diseases, or through damage incurred in a person's occupation. In discrimination tasks, such as two-point discrimination, the size of the change, or difference threshold, increases 1% every year from approximately 20 to 80 years of age. These losses are more pronounced on the extremities, such as the fingertip and big toe (Cohen, 1999).
In the relatively rare condition of neuropathy, large myelinated fibers in the peripheral nerves are lost, so inputs from muscle and many types of skin receptors are either nonexistent or severely limited. This condition usually results in a complete loss of kinesthesia in the affected limbs and a loss of the senses of touch, pressure, and vibration (Cohen *ROYS BOOK*, 1999).
Description of Semmes-Weinstein Monofilaments
In the 1890's, Von Frey found the need for an objective test of light touch. He finally discovered a method of measuring light touch using horsehair of varying stiffness sometime in the late 1890's. This was the method of choice until the 1960's and is still used to this day in some third world countries. In 1962, Semmes and Weinstein developed monofilaments based on the concept brought forth by Von Frey, using a material that bends when force is applied. (Waylett-Rendall, 1988.)
The Semmes-Weinstein monofilaments, available in sets of 5 or 20, are applied perpendicular to the skin and bend when they reach their threshold. A constant force is maintained by the monofilaments even while the fibers are bent. (Bell-Krotoski, Weinstein, S. & Weinstein, C., 1995.) The greater the diameter of the nylon material the greater the force applied to the area being tested. Three monofilaments commonly used to screen patients at risk for peripheral neuropathy are the 4.17, the 5.07, and the 6.10. Forces required to bend these monofilaments are 1, 10, and 75 g of force, respectively; however, if monofilaments are applied too quickly, they will buckle at a higher force. Protective sensation, or the ability to feel ulceration if one occurs, is indicative of the patient that is able to feel the 5.07 monofilament; however, protective sensation is still not the same as normal sensation. (Mueller, 1996) Thus, anyone who is not able to feel at least the 5.07 monofilament should be referred for further testing.
Reliability and Validity of Semmes-Weinstein Monofilaments
A foot and ankle evaluation is an important consideration for diabetic patients because of the frequency of injury to and disability of an injury to this area of the lower extremity. A foot injury can be quite debilitating, that is why sensation testing is highly useful in patients with diabetes. Results from past studies indicate that the Semmes-Weinstein testing proves to be a reliable and valid form of testing in this population of patients. A study conducted that used Semmes-Weinstein monofilament testing on elderly patients with diabetic neuropathy stated monofilament (kappa=.74; rs= .89â€.93) and QVPT (ICC=.77â€.94; SEM=3.4â€6.0 V; kappa= .74) testing demonstrated good to excellent inter-rater reliability. Another study stated that research indicates that the SW monofilament is an inexpensive, reliable, valid, and easy-to-use clinical indicator for identifying patients who are at risk for developing foot ulcers and ultimately amputations. Patients unable to feel the 5.07 SW monofilament on any part of their foot should be provided preventive care and referred out especially those not already diagnosed with Diabetes Mellitus. (Shaffer, 2005)
Normative Values of Semmes-Weinstein Monofilaments
In study conducted by Collins et al., the normative values for normal subjects were situated between monofilament 3.22 and 4.08 for the plantar aspect testing. Bell-Krotoski et al (1993) indicated that the set of five filaments is believed to be the minimum number of filaments that is recommended for screening abnormal versus normal.