Diabetic amyotrophy

Synonyms: Bruns-Garland syndrome, asymmetrical proximal diabetic neuropathy, lumbosacral plexopathy and diabetic lumbosacral radiculoplexus neuropathy

What is diabetic amyotrophy?

Diabetic amyotrophy is a diabetic proximal neuropathy. See also separate Diabetic Neuropathy article. Most (but not all) affected patients have type 2 diabetes.¹

What causes diabetic amyotrophy? (Aetiology)²

Diabetic amyotrophy is believed to result from a multifocal immune-mediated microvasculitis, ie an immune abnormality involving vasculitic changes, microvascular insufficiency and ischaemia followed by axonal degeneration and demyelination.³

Nerve biopsy shows multifocal nerve fibre loss suggesting ischaemic injury and perivascular infiltrate. It predominantly affects motor nerves of the lumbosacral plexus, particularly the femoral nerve, although autonomic and sensory nerves are also involved.^{3 4}

The condition is a diffuse axonal neuropathy. It falls within a spectrum of different neuropathic syndromes caused by or associated with diabetes. Their aetiology includes metabolic, compressive and inflammatory/immunological mechanisms.

They are discussed further in the separate Diabetic Neuropathy article and include:^{2 5}

• Generalised symmetrical polyneuropathies.

• Diabetic autonomic neuropathy, present to some degree in up to 75% of patients with type 2 diabetes.

• Focal neuropathies: mononeuropathies and entrapment syndromes - eg, median nerve neuropathy.

• Diffuse neuropathies: much less common but significant due to their severity and morbidity:

  • Axonal (mainly proximal - eg, diabetic amyotrophy). Most are lumbosacral but thoracic and cervical symptoms can occur.

  • Demyelinating (proximal and distal): chronic inflammatory demyelinating polyneuropathy (CIDP) is an immune-mediated disorder with primary damage to the myelin sheath. It is characterised by symmetrical, progressive weakness and paraesthesiae and tends to affect younger patients. It is closely related to GBS and is considered the chronic counterpart

How common is diabetic amyotrophy?(Epidemiology)⁶

The lifelong incidence of diabetic amyotrophy is estimated to be 1% among people with diabetes. It generally affects middle‐aged or elderly people with type 2 diabetes. It may occur soon after diagnosis or be the presenting complaint that leads to the diagnosis of diabetes mellitus.

Diabetic amyotrophy symptoms (presentation)^{1 2}

The main features of diabetic amyotrophy are weakness, wasting and pain, usually in the quadriceps. Symptoms begin on one side but usually spread to the other, although symptoms often remain asymmetric. Onset may be acute or subacute.

Patients with diabetic amyotrophy complain of pain (often severe), dysaesthesiae and paraesthesiae in the proximal lower limbs - usually the front of the thigh, hip or buttock. Pain may be also experienced in the lower back.

Weakness and wasting of thigh and leg muscles follow within days to weeks. Sensory impairment may be present but is minimal and occurs in the cutaneous distribution sharing the affected nerve root or peripheral nerve.

Weight loss occurs in more than half of patients. Stepwise progression occurs over months. In about 50% of patients, distal symmetrical polyneuropathy co-exists.

On examination there is proximal muscle weakness. Wasting in the quadriceps, hip adductors and iliopsoas muscles is characteristic. There is an absent or reduced knee jerk reflex, although ankle jerks are commonly preserved. Extensor plantar responses may be present and there may be mild sensory loss.

Some patients have symptoms of associated thoracic or cervical radiculopathy.⁵

Differential diagnosis

The differential diagnosis includes other causes of proximal neuropathy including:

• Cauda equina syndrome.

• Multiple sclerosis.

• Guillain-Barré syndrome (GBS).

• Spinal canal stenosis.

• Vitamin B12 deficiency.

• Alcohol dependency.

• Neoplastic lumbosacral plexopathy.

• Chronic inflammatory demyelinating polyneuropathy (CIDP).

The literature describes two cases of diabetic amyotrophy which were initially diagnosed as quadriceps tendon rupture, undergoing surgical repair. The authors say that quadriceps tendonitis should be viewed with caution in patients with diabetes.⁴

It is important to recognise that the condition can be the presenting feature of diabetes.³

Investigations²

• All patients not known to have diabetes and with a suspected peripheral neuropathy should have a random blood glucose test.

• Baseline haematinic studies to rule out vitamin B12/folate deficiency.

• Lumbar puncture if CIDP is suspected.

• Electromyography/nerve conduction studies show axonal damage in the classic form of proximal motor neuropathy. If it shows demyelination, a diagnosis of CIDP should be considered.

• MRI of lumbosacral spine to rule out structural and neoplastic disorders.

Diabetic amyotrophy treatment and management

Conservative treatment consists of optimising diabetic control along with very active physiotherapy and analgesia. Co-existing neuropathic pain is managed according to the usual neuropathic pain ladder.

Intravenous immunoglobulins have been found to produce improvement in both clinical and electrophysiological parameters in patients with some diabetic polyradiculopathies. Some reports have suggested they may be effective in diabetic amyotrophy.^{7 8 9}

However, a Cochrane review in 2017 concluded that there is presently no evidence from randomised trials to support any recommendation on the use of any immunotherapy treatment in diabetic amyotrophy.⁶

Prognosis

The condition usually runs a monophasic course that can be protracted (up to three years) with the pain and weakness often causing significant disability. Recovery of function occurs without medical treatment in nearly everyone but may be slow and incomplete.⁶

Weakness, sensory symptoms and absent tendon jerks may persist. Some patients experience multiple episodes but a minority of patients progresses to severe and persisting quadriparesis.^{3 10}

Dr Mary Lowth is an author or the original author of this leaflet.