AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

Ischemic monomelic neuropathy (IMN) is an infrequent problem that usually occurs after acute arterial occlusion or low blood flow to an extremity. This condition can occur after surgical procedures (for example, vascular surgery involving the thoracoabdominal aorta and its caudal arterial channels), as a result of the establishment of arteriovenous fistulas for hemodialysis access, or because of the development of arterial emboli or of thrombi.

Pathophysiology

IMN is primarily a problem of the distal nerves in an extremity; it is best thought of as multiple distal focal mononeuropathies involving the sensory and motor branches. The condition usually involves axonal nerve injury and is not a demyelinating process. Reversible motor conduction block in the forearm has been reported early in the course of IMN, but this block does not occur later in the disease. The muscle, skin, bone, and other tissues are spared. The nerves in the distal limb are most affected.

Frequency

United States

The frequency of IMN's occurrence is unclear because IMN has never been studied prospectively, and recognition of the problem varies. Given these limitations, IMN appears to be a rare condition, but it may be underreported. The Mayo Clinic reported only 32 patients with IMN from 1962-1987. Honet and colleagues, in a study reviewing the initial use of the intra-aortic balloon pump (IABP) in the early 1970s, reported a surprisingly high incidence of IMN.¹ Out of 39 patients who survived the initial use of the IABP, 6 of them were referred for leg problems that were diagnosed as IMN. Current use of the IABP is unlikely to have an incidence nearly this high. IMN can also occur after the establishment of arteriovenous fistulas for hemodialysis access, but again, the frequency of such incidences is unclear and unusual.

Mortality/Morbidity

Mortality is not associated with IMN; however, morbidity is significant. Depending on the severity of the injury, patients can be left with neurologic deficits that interfere with function and cause significant pain.

• In the hand, weakness of the thenar and intrinsic muscles has been reported. This weakness coexists with sensory loss in all fingers, which can extend proximally into the palm and hand.
• In the leg, weakness of the intrinsics is common, and weakness of ankle dorsiflexors and plantar flexors also is relatively common. Sensory loss in the foot and in the leg up to the midcalf is frequent as well. Pain in the areas of neurologic deficit is reported almost universally. This pain can be persistent or reversible, depending on the severity of the injury.
• The extent of disability from the above neurologic dysfunctions depends on the amount of nerve injury and may alter hand function or the ability to walk. For some patients, the pain associated with IMN is the most disabling aspect of the disease.

Race

No racial predilection is known to exist.

Sex

Male-to-female ratios have not been clearly documented. The risk for arteriosclerosis is slightly higher in males; therefore, the incidence of IMN is slightly greater in males.

Age

Because they are at higher risk for arteriosclerosis, elderly individuals are at much higher risk for IMN.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

The hospital is the most common place for presentation of IMN, which can vary depending on the location of the IMN.

• Patients with upper extremity IMN usually complain of pain in the hand and arm, with weakness in the hand. This pain generally occurs after hours of arterial occlusion of the brachial or subclavian arteries or following surgery to establish an arteriovenous fistula for dialysis graft access.
• IMN in the leg usually presents after hours of arterial occlusion, frequently following vascular surgery involving aortic occlusion (eg, abdominal aortic aneurysm repair, use of the IABP, revascularization surgery in the leg). Lower extremity IMN can also occur after prolonged tourniquet time in surgery or as a complication following arterial occlusion. If the patient is alert and not confused, he or she usually complains of pain in the foot and distal leg; the individual may also complain of weakness of toe movement and ankle dorsiflexion. Immediately after major surgery, it is common for patients to be confused, medicated, and/or not fully cognizant of problems in their legs that occurred during the surgery or as a result of cardiac events. Since the patients is confused, he or she does not complain of symptoms. In the meantime, the treatment team focuses on other pressing medical issues and does not notice the IMN. This results in a delay in diagnosisthat frequently lasts days or even weeks after the arterial occlusion has occurred.
• Chronic IMN has been reported in patients with chronic critical leg ischemia. The patients studied had angiographic documentation of severe large vessel stenosis or occlusion; they also suffered from limb pain while at rest or had nonhealing foot ulcers for more than 4 weeks. Distal foot and leg symptoms were present, along with some toe weakness.^{2, 3}

Physical

• Patients who have IMN in the arm usually have decreased sensation in all the fingers of the hand. Occasionally, the median or ulnar nerve territory is primarily affected. Allodynia or hyperesthesia in the distal radial, median, and ulnar nerve distribution is common. Frequently, weakness of the abductor pollicis brevis and the intrinsic muscles of the hand is exhibited. Occasionally, more proximal musculature can be affected (wrist flexors or wrist extensors), but this pattern is exceedingly rare.
• Physical examination of the leg frequently shows decreased sensation in the foot and distal calf. Allodynia and hyperesthesia also may be present. Intrinsic wasting in the feet is usually present. Distal leg muscles also can be weak, including the extensor hallucis longus, anterior tibialis, peroneus longus, and gastrocnemius/soleus. In rare cases, the hamstrings, quadriceps, and hip abductors are affected. Gait may be abnormal in that the patient may have steppage gait associated with ankle dorsiflexion weakness (foot drop). Reflexes may be asymmetric, especially at the ankle, with an absent Achilles reflex in the affected leg.
• In cases of chronic disuse, contractures of the distal joints (fingers, toes, wrists, or ankles), with swelling, skin atrophy, and vasomotor changes, can be present. These conditions can coexist with complex regional pain syndrome (CRPS) type 2 (also known as reflex sympathetic dystrophy [RSD]).
• Patients with chronic IMN most commonly have hypalgesia in their distal foot and toes and/or nonhealing skin ulcers.

Causes

Upper Extremity 

The primary causes for IMN in the arm include any problem that causes a hypercoagulable state, as well as thoracic outlet obstruction (with angiographic confirmation), trauma or laceration of the brachial artery, intra-arterial injection, and cellulitis. A shunt for an arteriovenous fistula also can be a culprit; most cases have been described in patients with diabetes, thus confounding the development of IMN superimposed on diabetic polyneuropathy.

Lower extremity

Risk factors include any problems that interrupt and cause acute arterial occlusion. These factors can include hypercoagulable states, methysergide (a vasoconstrictor used for migraine), cannulization of the femoral artery, aortic occlusion from arteriosclerotic vascular disease, abdominal aortic aneurysms, peripheral vascular disease, low cardiac output, IABP, or prolonged tourniquet time in surgery. The limb that has been cannulated for the IABP or for cardiopulmonary bypass is particularly susceptible to IMN.

• In chronic IMN, the etiology is peripheral vascular disease.
• Upper and lower extremity IMN can be related to noniatrogenic and iatrogenic causes.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to Be Considered

Cauda equina syndrome
Peripheral polyneuropathy

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

• Hours to days after the onset of IMN, an elevated creatine kinase level can be noted from muscle necrosis.

Imaging Studies

• Depending on the clinical presentation, vascular studies that detect acute arterial occlusion may be useful. Because IMN usually is not the presenting problem but more a complication that occurs after previous arterial occlusion, work up and/or treatments (eg, arteriogram, surgeries) already have been completed.
• In confusing clinical situations, imaging studies sometimes are necessary to rule out upper motor neuron problems (eg, stroke, spinal cord injury).
• Other imaging studies that can be helpful, depending on history, include arteriograms and venous or arterial Doppler studies. These tests can help to include vascular occlusion in or to exclude it from the diagnosis. With an arteriovenous fistula in the upper extremity, a Doppler study to assess for vascular patency can be helpful.
• Electrodiagnosis establishes the pattern of peripheral nerve injury. If the findings are not consistent with IMN, additional diagnostic studies may be warranted.
• In chronic IMN, results from vascular studies are abnormal and show arterial occlusion in 1 leg.

Other Tests

• Upper extremity electrodiagnostic evaluation
• • Abnormalities are seen in a proximal-to-distal pattern, and the distal nerve supply is affected much more than any other. Radial, median, and ulnar sensory nerve action potentials (SNAPs) usually are absent from the respective digits. More proximal SNAPs (medial antebrachial cutaneous, lateral antebrachial cutaneous) are likely to be present.
  • Motor nerve conduction from the median and ulnar nerves to the hand muscles is absent or has a low amplitude. Nerve conduction velocities, when present, are spared to a relative extent.
  • Needle electromyography shows evidence for axonal loss with positive sharp waves and fibrillation potentials in the hand muscles (median and ulnar innervation). If the lesion is severe, there may be no recruitment or evidence of decreased (neuropathic) recruitment. Evidence for reinnervation can be seen months to years after the nerve injury, including large motor unit action potentials (MUAPs) and/or polyphasic motor units. In complete injuries, there is scarring in the muscle, with decreased insertional activity. Needle electromyography is typically normal or less severe in proximal muscles (forearm and upper arm). This clear distal-to-proximal gradient is in contrast to a brachial plexopathy.
  • For the diagnosis of IMN to be clear, 1 arm needs to demonstrate significantly more injury than the other arm. In cases of severe diabetic neuropathy, where both arms are affected equally, it is essentially impossible to make the diagnosis of an IMN that is superimposed on a severe polyneuropathy. For example, it can be difficult to differentiate a lower trunk plexopathy from an IMN in the hand. A lower trunk plexopathy generally shows severe abnormalities in the intrinsic muscles of the hand on electromyography, low compound motor action potentials (CMAPs) from the median and ulnar nerves, and an absent SNAP.
  • The major differentiation in the hand is that, in a lower trunk plexopathy, the radial SNAP and median SNAPs to the fingers probably are spared, while the medial antebrachial cutaneous SNAP is absent. In IMN, the median and radial SNAPs are absent, and the medial antebrachial cutaneous SNAP is spared. With a lower trunk plexopathy, needle electromyography abnormalities in the flexor carpi ulnaris, triceps, and extensor indices are expected; in IMN, the abnormalities of these proximal muscles are absent or minimal.
• Lower extremity
• • SNAPs to the sural and superficial peroneal commonly are absent. CMAPs to the abductor hallucis and peroneal nerve to the extensor digitorum brevis are either absent or low in amplitude. Nerve conduction velocities are relatively spared, if they can be measured. In IMN, H-reflexes and CMAPs elicited from the tibial nerve at the gastrocnemius and from the peroneal nerve at the anterior tibialis are frequently normal or near normal.
  • Needle electromyography frequently shows marked abnormalities consistent with axon loss in foot intrinsic musculature and lesser findings in the anterior tibialis, gastrocnemius, and soleus. Abnormalities in the quadriceps, hamstrings, or gluteal muscles generally are not observed, although they have been reported.
  • As in the upper extremity, differentiation of the normal limb from the abnormal limb is helpful in diagnosing IMN. In severe peripheral polyneuropathies, primarily distal ones, findings can be very similar or identical to those of IMN. The diagnosis of IMN is contingent on a normal or near-normal contralateral limb. Occasionally, distal aortic occlusion with saddle emboli can cause bilateral IMN, or use of the IABP pump in both legs can contribute. In mild cases of IMN, electromyographic abnormalities (positive sharp waves and fibrillation potentials) have been seen only in the foot intrinsic muscles.
  • Differentiation of IMN from an L5-S1 or S2 radiculopathy or sciatic nerve neuropathy can be difficult. In IMN, the distal L5-S2 muscles have severe abnormalities, while the more proximal L5-S1 (gluteus medius, tensor fasciae lata) are likely to be normal or have minimal abnormalities. The tensor fasciae lata or gluteal muscles rarely are involved in IMN; in an L5-S2 radiculopathy, the tensor fasciae lata and/or gluteus medius should show similar abnormalities to the more distal L5-S2 muscles. This finding differentiates IMN from a plexopathy or radiculopathy.
  • In chronic IMN, the most common electrodiagnostic abnormality is a decreased CMAP in the tibial nerve to the abductor hallucis. Because the disease is chronic, both of a patient's legs can be affected, and the sural responses may be abnormal unilaterally or bilaterally. Quantitative sensory testing results have been reported to be abnormal in the distal foot.
• Occasionally, compartment pressure measurements are indicated immediately following the ischemia if there is a concomitant compartment syndrome.

Procedures

• IMN does not require any direct procedures. Various procedures may be needed to treat other associated conditions.

Histologic Findings

Tissue biopsies rarely are taken after IMN and are not reported to be helpful in its diagnosis.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Rehabilitation Program

Physical Therapy

Rehabilitation measures to assist with recovery after IMN depend on the degree of nerve injury. An aggressive and appropriate range of motion (ROM) program can prevent contractures in the involved limb. Thermal agents should be used with caution, given concomitant sensory impairments. For gait activities, a double metal upright or solid plastic ankle-foot orthosis (AFO) may be indicated if there is poor control of ankle and foot movement.

Occupational Therapy

An aggressive and appropriate ROM program, particularly in the hands, can prevent contractures. Working to improve activities of daily living (ADL) is important, and adaptive equipment may be beneficial in aiding independence.

Medical Issues/Complications

Few predictable medical problems are associated with IMN.

Surgical Intervention

Surgery has little to offer in established IMN. In cases of acute thrombosis or compartment syndrome, surgical intervention may be beneficial.

Consultations

Evaluation by a physiatrist can help in the diagnosis, treatment, and rehabilitation of IMN.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Neuropathic pain may be quite debilitating in IMN, although it is uncertain how frequently it presents. The medications for neuropathic pain include anticonvulsants, antidepressants, local anesthetics, and opioids.

Drug Category: Anticonvulsants

Use of certain antiepileptic drugs, such as the GABA analogue gabapentin (Neurontin), has proven helpful in some cases of neuropathic pain. These drugs have central and peripheral anticholinergic effects, as well as sedative effects, and block the active reuptake of norepinephrine and serotonin. The multifactorial mechanisms of analgesia could include improved sleep, altered perception of pain, and increase in the pain threshold.

Drug Category: Antidepressants

These are complex group of drugs that have central and peripheral anticholinergic effects, as well as sedative effects. They have central effects on pain transmission. They block the active reuptake of norepinephrine and serotonin.

Drug Category: Opiates

These agents may decrease neuropathic pain; they should be used to decrease pain, increase function, and improve quality of life. The side effects of cognitive difficulties, tolerance, addiction, nausea, and other problems need to be taken very seriously. Use of contracts to assure the appropriate use of opiates and that link the use of opiate medication to good behavior are helpful. If a patient's behavior deteriorates, consider decreasing or discontinuing the opiate medication because it may be contributing to the problem. Use of opiates only at night to improve sleep may be the most effective use of these medications for the long-term treatment of neuropathic pain.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Further Inpatient Care

• Inpatient care for patients with IMN is 2-fold. Patients with IMN may have numerous comorbid medical and surgical problems that require monitoring and interventions. If the IMN significantly interferes with wrist/hand or ankle/foot function, occupational therapy and physical therapy services are warranted under the direction of physiatry specialists.

Further Outpatient Care

• Further outpatient care is a continuation of rehabilitation goals and may include functional mobility training, preservation of ROM, education with regard to limb care, and pain management.
• Psychological counseling to assist with adjustment to disability also may be warranted.

In/Out Patient Meds

• No medications are specific for IMN. Medications used to treat neuropathic pain may be helpful.

Prognosis

• The prognosis depends on the amount of initial nerve damage. Functional improvement in the leg is expected, because the nerve regenerates at 1 in/mo (2.5 cm/mo). In the leg, persistent weakness of the ankle and toe musculature is frequent. Occasionally, there is weakness of knee extensors and flexors. Sensation in the foot and distal leg can remain permanently impaired. Contractures of the paralyzed or weakened joints are frequent.
• The prognosis for the arm is similar to that for the leg. The nerve regenerates at 1 in/mo (2.5 cm/mo). Distal weakness and sensory loss, with contractures of weakened joints, especially in the fingers, are possible.
• Residual pain may be the most troubling problem following nerve regeneration and rehabilitation.

Patient Education

• As with all medical conditions, explaining the problems associated with nerve injury can help patients cope with issues related to the disorder and with rehabilitation.
• Patients should be instructed to care meticulously for their insensate skin areas in order to prevent skin breakdown.
• Patients should continue with an ROM exercise program.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Proper diagnosis of IMN as a vascular lesion can avoid incorrect classification of the injury as a plexus or a root lesion from trauma, as well as avoid incorrect positioning during surgery.
• IMN has been involved in legal cases as a complication of orthopedic or cardiovascular surgery.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

1. Honet JC, Wajszczuk WJ, Rubenfire M, et al. Neurological abnormalities in the leg(s) after use of intraaortic balloon pump: report of six cases. Arch Phys Med Rehabil. Aug 1975;56(8):346-52. [Medline].
2. Chroni E, Papapetropoulou V, Tsolakis J, et al. Chronic ischemic monomelic neuropathy from critical limb ischemia. Neurology. Jun 11 2002;58(11):1705; author reply 1705-6. [Medline].
3. Weinberg DH, Simovic D, Isner J, et al. Chronic ischemic monomelic neuropathy from critical limb ischemia. Neurology. Sep 25 2001;57(6):1008-12. [Medline].
4. Andary MT, Fankhauser MJ, van der Harst CL. Ischemic monomelic neuropathy with involvement of sacral nerves and sparing of sympathetic skin response. Muscle Nerve. 1993;16(10):1105(A).
5. Bolton CF, Driedger AA, Lindsay RM. Ischaemic neuropathy in uraemic patients caused by bovine arteriovenous shunt. J Neurol Neurosurg Psychiatry. Sep 1979;42(9):810-4. [Medline].
6. Chalk CH, Dyck PJ. Ischemic Neuropathy. In: Dyck PJ, Thomas PK, Griffin JW, et al, eds. Peripheral Neuropathy. vol 3. Philadelphia, Pa: WB Saunders; 1993:980-9.
7. Hye RJ, Wolf YG. Ischemic monomelic neuropathy: an under-recognized complication of hemodialysis access. Ann Vasc Surg. Nov 1994;8(6):578-82. [Medline].
8. Lachance DH, Daube JR. Acute peripheral arterial occlusion: electrophysiologic study of 32 cases. Muscle Nerve. Jul 1991;14(7):633-9. [Medline].
9. Levin KH. AAEE case report #19: ischemic monomelic neuropathy. Muscle Nerve. Oct 1989;12(10):791-5.
10. Rabbani MA, Ahmad B, Shah SM, et al. Ischemic monomelic neuropathy: a complication of vascular access procedure. J Pak Med Assoc. Sep 2005;55(9):400-1. [Medline].
11. Riggs JE, Moss AH, Labosky DA, et al. Upper extremity ischemic monomelic neuropathy: a complication of vascular access procedures in uremic diabetic patients. Neurology. Jul 1989;39(7):997-8. [Medline].
12. Schmidt FE, Hewitt RL. Severe upper limb ischemia. Arch Surg. Oct 1980;115(10):1188-91. [Medline].
13. Wytrzes L, Markley HG, Fisher M, et al. Brachial neuropathy after brachial artery-antecubital vein shunts for chronic hemodialysis. Neurology. Aug 1987;37(8):1398-400. [Medline].

Article Last Updated: Sep 14, 2007