January 11th - LBJ - Polymyositis/Dermatomyositis and Rheum Labs

Today at LBJ a case of Polymyositis was presented

Here is an overview of the inflammatory myopathies and some rheum labs to know for boards








The 3 Inflammatory Myopathies you should know about for boards are Polymyositis, Dermatomyositis and and Inclusion Body Myositis

Clinical
Polymyositis and Dermatomyositis: Proximal Muscle Weakness.  Classically they have difficulty "rising from a chair." Also they can have trouble lifting their head up and trouble climbing stairs. 
Pain is not frequently present in these patients (myalgias in less than 30%), it is more muscle weakness.  Arthralgias may be present, and pharyngeal weakness can lead to dysphagia/aspiration. 
Dermatomyositis is essentially Polymyositis with a rash, but with more to know on this in a bit

Diagnostic Criteria:
1. Symmetrical weakness of limb girdle muscles
2. Muscle Biopsy showing necrosis and perifasicular atrophy
3. Elevated Muscle Enzymes (Can be any - CK, Aldolase, LDH and AST are the most often used)
4. EMG with small action potentials, sharp waves and high frequency discharges

Definite Polymyositis is all 4 above
Definite Dermatomyositis is 3/4 above + Skin/Rash Findings c/w disease

                               So what are the skin/rash findings... There are many. For boards, you'll need to know:

                                                    Gottren's Papules - purple/scaly eruption over the MCPs

Heliotrope Rash - purple discoloration of upper eyelids

Shawl Sign - photosensitive erythema on anterior chest

So, like stated Dermatomyositis is clinically polymyositis with the skin changes. 

Workup/Labs:

Your workup for these patients will be what is necessary to help diagnose (i.e EMG).

Muscle biopsy is done, but usually after MRI - so they know where to target the biopsy

CXR should be checked at the time of diagnosis to look for Interstitial Lung Disease

ANA is Positive in >90 of Patients

Anti-Mi2 can be present in Dermatomyositis (<25% of the time)

Anti-Jo1 can be present in Polymyositis - and when this is present patients is known to "antisynthetase antibody syndrome) - characterized by polymyositis, arthritis, interstitial lung disease, fever, Raynaud's and

"mechanics hands" (a dry scaly rash on the fingers)

Other antibodies may be positive if there is an overlap syndrome present (more on this later)

Complications:

- Like stated before, pharyngeal involvement can lead to aspiration

- Patients can get cardiomyopathy or arrythmias from cardiac involvement

- Interstitial lung disease is a complication as well

- Malignancy:  not so much a complication, but a disease association.  Especially in patients with Dermatomyositis, there is evidence that a workup for malignancy should be done.  The most common malignancies found in these patients are ovarian, lung and head/neck. So, a good screening/workup should be done in patients with Dermatomyositis.  CT scanning of the Chest, Abdomen and Pelvis are usually done

Treatment:

Initially with High Dose Prednisone (1-2 mg/kg/day) which is continued until elevated enzymes decrease

After these values begin to decrease, the dose is tapered to maintenance of 5-10mg daily.  Steroid sparing agents (i.e. MTX or AZA) can be used.  Hydroxychloroquine can be used for the skin lesions. 

Inclusion Body Myositis:

All you need to know is that this occurs in patients that are older than 50 years, and patients have DISTAL muscle weakness> Proximal weakness.  Dyphagia is usually present as well (greater than 50% of patients).  Concominant cardiovascular disease is usually present in these patients, but may be due to their age on diagnosis.  Muscle Biopsy is diagnostic.  Sometimes it is precipitated by drugs such as alcohol and cocaine. To treat, stop offending agent and can give steroids, but they don't help too much.

For Boards, here is a quick Antibody Review For You:
ANA - Positive is so many things....  SLE, Scleroderma, Sjogrens, Mixed Connective Tissue, Myopathies

Anti-Histone - Drug Induced Lupus... Remember these patients have the same clinical findings as in regular Lupus, but the CNS are Renal findings are rare

Anti-CCP - Diagnose/Send in patient with early RA

RF - Rheumatoid Arthritis

Anti-Jo1 - Antisynthesase Syndrome

Anti-Mi2 - Polymyositis

Anti-Smith - Specific Test for SLE. Good to Send for Flare.

Anti-dsDNA - SLE. Good to Send for Flare. Predicts Renal Involvement

Anti-U1 RNP - Mixed Connective Tissue Disease - Patients get SLE + Polymyositis + Scleroderma

SSA (Anti-Ro)  and SSB (Anti-LA) - Sjogren's and SLE. SSA with Neonatal Lupus too. 

Anti-scl70 - Diffuse Scleroderma

Anti-Centromere - CREST Syndrome (i.e. Limited Scleroderma)

c-ANCA - Wegeners

p-ANCA - Churg-Strauss and microscopic Polyangiitis.  These two are also MPO +: know that there are diseases which are p-ANCA positive and MPO Negative (such as ulcerative colitis and hepatitis)

Anti-Mitochondrial - Primary Biliary Cirrhosis

Anti-Smooth Muscle - Autoimmune Hepatitis (patients are usually ANA positive as well)

Reference:
Images Courtesy of
Picasaweb: picasaweb.google.com/.../6sgfojHcfP1D90x2j_2ANw
Emedicine: emedicine.medscape.com/article/332783-overview
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