Middle-aged Man With Worsening Foot Pain

For about 3 to 4 months, a 53-year-old man has had gradually worsening footdiscomfort. He describes the discomfort as a burning sensation accompaniedby numbness and tingling. Initially, these symptoms were present only in hisfeet, but for several weeks they have involved both ankles as well. Althoughthe discomfort is always present, it is occasionally aggravated by the bed coversor by heavy woollen socks. The patient has no skin lesions, motor symptoms,or other abnormalities of his legs or feet.HISTORY
The patient takes no long-term medications, does not smoke, and consumesno more than 1 or 2 ounces of alcohol per week. He has worked all hisadult life as an accountant. A review of systems reveals increased nocturia(3 or 4 times each night).PHYSICAL EXAMINATION
The patient is obese; he is 177 cm (69 in) tall and weighs 125 kg (275 lb).Cranial nerves are intact, and there is no paresis in any extremity. Ankle reflexesare diminished bilaterally. Proprioception is also reduced in both feet and inboth legs to midcalf. The remainder of the physical examination is normal.Which of the following laboratory findings correlates best with thispatient's symptoms?A.Abnormal sural nerve biopsy results that reveal the presence ofMycobacterium leprae.B. Abnormal fasting glucose level and glycosylated hemoglobin level,consistent with diabetes mellitus.C. Abnormal lead and protoporphyrin levels, consistent with leadintoxication.D. Elevated erythrocyte sedimentation rate and cryoglobulin studies,consistent with polyarteritis nodosa.CORRECT ANSWER: B
Peripheral neuropathy is commonly seen in clinicalpractice. Once it has been determined that symptoms areassociated with peripheral nerve pathology (in contrast to,for example, rheumatologic conditions, such as plantarfasciitis, tendinitis, and bursitis), the next step is to distinguishbetween small fiber neuropathies and the variouslarge fiber neuropathies.In small fiber neuropathies, symptoms include sharppain and burning. Both symptoms may also be present inlarge fiber neuropathies;however,there are frequentlyadditionalfeatures, suchas tingling,numbness, nocturnalexacerbation,and exacerbationwith tightfootwear. Physicalexaminationfindings are oftencompletely normalin patientswith painfulsmall fiber neuropathy;in thosewith large fiberneuropathy, abnormalfindings(eg, reduced proprioception, loss of muscle stretch reflexes,and muscle weakness) are frequently noted.The diagnostic test most commonly used to distinguishbetween small fiber and large fiber neuropathies is anerve conduction study.¹ Electromyography is also useful.Small fiber sensory neuropathy is the most commonpainful neuropathy in patients older than 50 years. In thevast majority of patients, no underlying cause is found.¹Large fiber sensorimotor neuropathies, on the otherhand, frequently have an underlying cause. It is importantto know the cause both because of its own treatment requirementsand because the neuropathy occasionally resolves--or at least improves--when the underlying conditionis treated. The most common causes of large fiberneuropathy are excessive alcohol consumption, diabetesmellitus, and HIV infection.²Differential diagnosis. Ischemic neuropathies, suchas mononeuritis multiplex and the neuropathies associatedwith polyarteritis nodosa (choice D), are frequently asymmetrical,have a more dominant motor component, andtypically have a more acute onset than that described here.Leprosy (choice A) may be the most common treatableneuropathy worldwide; however, there is no travelhistory or any other clue to suggest that diagnosis here.This patient had chronic symptoms that worsenedover weeks to months. This is the hallmark of most toxicand metabolic neuropathies. Lead neuropathy (choice C)is a predominantly motor neuropathy, although it may beassociated with pain. Classic signs in adults include wristand/or foot-drop that result from the involvement of radialand peroneal motor nerves. An exposure--typically occupationalin adults--is usually readily evident in the history.None of these findings are seen here.Diabetic neuropathy (choice B) is a strong possibility.The chronic course of this man's complaints (weeks tomonths) is consistent with a metabolic cause, and his nocturiais a strong clue to the presence of diabetes. Thus, ofthe possible answers, diabetes is most consistent with thefindings in this patient.Outcome of this case.Electromyography and nerveconduction studies confirmed the presence of a large fiber,mixed sensorimotor neuropathy. A random blood glucoselevel was 173 mg/dL; the patient's glycosylated hemoglobinlevel--7.5%--confirmed the diagnosis of diabetes mellitus.He was initially given gabapentin, 900 mg/d, whichameliorated his symptoms. An American Diabetes Association1500 Kcal/d diet was also prescribed. Further decisionsregarding therapy will be made after the patient hasattempted to lose weight and has received symptomatictherapy for the neuropathy.

References:

REFERENCES:

1.

Mendell JR, Sabenk Z. Painful sensory neuropathy.

N Engl J Med.

2003;348:1243-1255.

2.

Backonja M, Beydoun A, Edward KP, et al. Gabapentin for the symptomatictreatment of painful neuropathy in patients with diabetes mellitus: a randomizedcontrolled trial.

JAMA.

1998;