22 - Diabetic Myonecrosis

Question 1

How does our patient with diabetic myonecrosis present?

Answer 1

• 42 year old Burmese refugee seen for 2 months of left calf and thigh pain and swelling
• He has been in the US for 1 year-prior to that spent 1 year in a Thai refugee camp
• Denies recent trauma, but does relate developing calf pain while walking to Thailand (about 200 miles)

Question 2

What is the past medical history of our patient with diabetic myonecrosis?

Answer 2

• Type II diabetes mellitus of 4 years duration-last glycohemoglobin (6 months previously) was 9.6%
• Hypertension
• Hypercholesterolemia

Taking humulin 70/30, simvastatin, lisinopril and aspirin

Question 3

What do we find on physical exam in our patient with diabetic myonecrosis?

Answer 3

• Pedal pulses are ¼ bilateral and symmetrical

- Capillary fill time is

Question 4

What is on the differential list at this point?

Answer 4

• Achilles or calf injury
• Fracture
• DVT
• Tumor
• Muscle infection (pyomyositis)
• Trichinosis
• Diabetic amyotrophy (proximal diabetic neuropathy)
• Compartment syndrome
• Rhabdomyolysis
• Diabetic myonecrosis

Question 5

What tests do you want to order?

Answer 5

• CBC
• Sed rate
• Metabolic panel
• X-ray of calf
• Duplex doppler ultrasound for DVT

Question 6

All of these are negative… Now what?

Answer 6

MRI

• Insurance companies will never let you get an MRI first
• Need X-ray first
• Anything with metal will rip out (welder, shrapnel, bullets, etc.)
• Does not affect orthopedic hardware

Question 7

Describe what you are looking at when you see a T1 MRI image

Answer 7

T1 image

• Fluid is BLACK
• This is called “hypointense”

We see some black in the image, so there is some fluid accumulation

Question 8

Describe what you are looking at when you see a T2 MRI image

Answer 8

T2 image

• Fluid is WHITE
• This is called “hyperintense”

We see a lot of white here, so we know there is fluid present in the muscle

Question 9

Given this information, what do we know?

Answer 9

There is fluid in the leg - could be an abscess (pyomyositis)

The next step is to use IV gadolinium to see if it is an abscess

IV gadolinium on a T1 will show a dark central area surrounded by a bright rim ***

Question 10

What would we see if we used IV gadolinum and there was an abscess?

Answer 10

IV gadolinium on a T1 will show a dark central area surrounded by a bright rim

Question 11

Is this what we saw on the MRI?

Answer 11

NO

• We viewed non-infectious muscle
• There was an absence of a uniform central area of decreased signal
• There was no uniform “rim” sign either
• This is NOT an abscess

Question 12

Since we ruled out an abscess, what can we conclude?

Answer 12

This is a diabetic myonecrosis

Diabetic myonecrosis is a rare complication of diabetes. It is caused by infarcted muscle tissue, usually in the thigh but can also be in the calf

Question 13

What are the clinical features of diabetic myonecrosis?

Answer 13

• Pain and swelling in anterior thigh (80%) or calf (20%)

- No specific laboratory marker, except leukocytosis seen in

Question 14

What is the pathogenesis of diabetic myonecrosis?

Answer 14

Vascular disease and hypercoagulability

Vascular disease

• Ischemia
• Soft tissue swelling
• Increased pressure in the leg
• Decreased blood flow

Hypercoagulability

• Increased factor VII activity
• Increased levels of tissue plasminogen activator inhibitor and thrombomodulin
• Impaired response of tissue plasminogen activator to venous occlusion
• Cases of antiphospholipid syndrome have been found as etiology

Question 15

What is the most valuable technique for diagnosing diabetic myonecrosis?

Answer 15

MRI

Question 16

What are you looking for in an MRI to diagnose diabetic myonecrosis?

Answer 16

T1

• Isointese or hypointense (dark) images due to increased water
• Increased bright white (fluid) when gadolinium-enhanced T1 images are used

T2

• Increased bright white (fluid) in the intramuscular and perimuscular areas
• You may be able to see a small focal area of rim enhancement ***
• This represents the infarcted or necrotic rim around the fluid filled area

Question 17

What is the difference between rim enhancement and rim signal

Answer 17

• A rim signal is a bright white halo around an abscess

- Rim enhancement is just a little area of light

Question 18

Are any other tests as reliable as MRI?

Answer 18

No

X-ray, ultrasound, CT, nuclear scans, EMG, biopsy are not as reliable as MRI

Biopsy is probably more of a gold standard than MRI, but you don’t want to go in there unless you have to, so MRI is used more

Question 19

What is the treatment for diabetic myonecrosis?

Answer 19

Supportive

• Rest
• Analgesia (pain management)
• It is a self-limiting disease

Question 20

What are the conclusions we need to remember from this case study?

Answer 20

• Often missed, but rare finding
• Occurs in poorly-controlled diabetics
• Consider dx in any diabetic with thigh pain and swelling ***
• MRI is diagnostic modality of choice***
• Biopsy is “gold standard” for diagnosis, but should be avoided due to possible complications***
• Treatment is supportive; symptoms resolve in weeks to months

Question 21

Describe the risk of recurrence of diabetic myonecrosis

Answer 21

• Risk of recurrence in ipsalateral or contralateral leg is high
• Long term prognosis poor, since myonecrosis is a marker for significant systemic vascular complications
• Check patient for retinopathy, nephropathy, carotid and cardiac disease

Question 22

What is the image you NEED to be able to recognize?

Answer 22

An abscess

• This image is a T1 using IV gadolinium ***
• The gadolinum is a contrast medium
• You will have a homogenously dark area in the muscle surrounded by a white rim
• This means there is an infection (an abscess)

Slide 17 –> RECOGNIZE THE IMAGE
- It is an infection (pyomyositis)