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Michael Polydefkis, M.D. M.H.S.
04-30-2010
- An underdiagnosed condition referred to by different names including "diabetic proximal amyotrophy", "diabetic lumbosacral plexopathy", "diabetic lumbosacral radiculoplexopathy", "ischemic mononeuropathy multiplex", "femoral-sciatic neuropathy", "femoral neuropathy", "diabetic cachexia" and "Bruns-Garland syndrome".
- Classically, a monophasic illness characterized by acute or subacute, progressive, asymmetrical lower limb muscle weakness (i.e. back, buttocks or thigh) a few weeks after severe pain onset with variable degrees of recovery.
- Patients typically also have diabetic peripheral neuropathy (DPN).
- Differentiated from diabetic polyneuropathy by the spatial pattern of involvement, time course, and prominent motor involvement (see Symptoms and Diagnosis sections).
- Important to diagnose diabetic amyotrophy (DA) because treatment differs from DPN.
- Epidemiology not well established, but overall prevalence estimated at ~1%; more common in T2DM than T1DM.
- Classically occurs in middle- to older-aged adults, but also described in children.
- Increasing evidence that an immune-mediated inflammatory microvasculitis, resulting in ischemic nerve damage, may be the underlying pathogenic process (Chan).
- Often associated with poor glycemic control.
- Diagnosis based on clinical presentation, distinction from DPN and electrodiagnostic testing.
- Hallmark is proximal lower extremity weakness, that may be asymmetric.
- Electrodiagnostic findings: multifocal denervation in paraspinous & leg muscles on EMG and reduced sensory and motor action potentials on nerve conduction testing.
- Nerve biopsy: rarely required to make the diagnosis. Pathologic findings notable for ischemic injury and microvasculitis, prompting physicians to treat DA with immunomodulating therapies when diagnosed early, although no evidence of benefit (Chan).
- Lumbar puncture: CSF protein often elevated.
- MRI: imaging of the lumbar spine and lumbosacral plexus can be helpful to exclude infiltrating disorders in subacute cases.
- Conditions that can mimic DA include ALS, mononeuropathy multiplex, limb girdle muscular dystrophy, acute radiculopathies and other plexopathies such as carcinomatous infiltration or radiation plexitis.
- Pain is severe; even stoic patients may seek emergency care and requiring multiple agents including opiates.
- Weakness also not subtle and typically 50% of patients will be wheelchair-dependent
- Proximal leg muscles weakness (quadriceps, hip flexors, extensors) compared to distal sensation abnormalities in DPN.
- Knee reflex usually absent
- Symptoms progress over months; mean 6.2 months in one case series (Bastron)
- However, duration may be variable, ranging from a few months to several years.
- Usually unilateral, though it can be bilateral or even involve thoracic nerves.
- Patients often have substantial concomitant weight loss that approaches 50 lbs.
- Rarely a presenting complication of diabetes.
- Early diagnosis critical for therapeutic intervention such as steroids or intravenous immunoglobulin (IVIg).
- Immunotherapy options consist of IVIg or IV methylprednisolone (MP). MP will increase blood glucose or insulin requirement (see steroids in diabetes module) and IVIg carries risk of acute renal failure. Patients with GRF<50 ml/min should be especially well hydrated and monitored closely.
- Recovery occurs more slowly without medical treatment, although definitive evidence is lacking due to the rarity of the condition.
- Treatment is otherwise largely supportive, including pain medication and physical therapy. Hospitalization is rarely needed.
- Treat patients who become wheelchair or bed-bound for risk of DVT.
- Patients may require subacute rehabilitation and outpatient physical therapy.
- Most have a good functional recovery within 12-24 months. Occasional relapses can occur.
- Little evidence that glycemic control affects prognosis, although it is anecdotally recommended.
- Most important to recognize and diagnose DA, and distinguish it from DPN.
- While DA is more alarming compared to DPN, the prognosis is better
- Patients with DA typically do improve spontaneously, though we, and most neurologists do treat with IVIg or IV methylprednisolone when diagnosed early.
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