Polymyositis and Dermatomyositis Flashcards
Muscle Disease
What is polymyositis?
An idiopathic inflammatory myopathy causing symmetrical, proximal muscle weakness
How does dermatomyositis differ from polymyositis?
Dermatomyositis includes cutaneous manifestations in addition to muscle weakness
What is the common age and gender affected by polymyositis/dermatomyositis?
Females (2:1 ratio)
Peak incidence ages 40-50
What is the key autoimmune mechanism in polymyositis?
T cell-mediated attack on muscle antigens, involving CD8+ T cells and macrophages
What are the main clinical features of polymyositis?
(1) Symmetrical
(2) proximal muscle weakness with gradual onset
What is Gottron’s sign?
A rash over the knuckles
= characteristic of dermatomyositis
Name an antibody associated with interstitial lung disease in myositis patients
Anti-Jo-1 antibody
First-line investigation for polymyositis and dermatomyositis?
Blood test for creatine kinase (CK)
= typically elevated
What is the gold standard diagnostic test for polymyositis/dermatomyositis and why?
Muscle biopsy
= shows perivascular inflammation and necrosis
What is the primary treatment for polymyositis/dermatomyositis?
Prednisolone (first-line)
with the possible addition of methotrexate or rituximab if unresponsive
What are common cutaneous signs in dermatomyositis?
Gottron’s sign
Heliotrope rash
Shawl sign
What are the first and second-line treatments for polymyositis and dermatomyositis?
First-line
= Prednisolone +/- methotrexate
Second-line
= Rituximab or other immunosuppressive therapies
Name a syndrome associated with myositis and its key features
Anti-synthetase syndrome
= includes
(1) mechanic’s hands
(2) raynaud’s phenomenon
(3) myositis
(4) interstitial lung disease
(5) polyarthritis
What symptom may suggest early dermatomyositis involvement?
Difficulty with activities like brushing hair or climbing stairs due to proximal muscle weakness
What physical tests assess muscle strength in myositis?
(1) Confrontational testing
(direct power)
(2) Isotonic testing
(eg, 30-second sit-to-stand)
What is the “shawl sign” in dermatomyositis?
A reddish-purple rash over the shoulders and upper back
Which muscle enzyme is a key indicator of disease activity in polymyositis and dermatomyositis?
Creatine kinase (CK)
How can dermatomyositis be present on the hands?
Gottron’s papules (scaly, erythematous knuckle lesions)
Name two myositis-specific autoantibodies.
Anti-Jo-1 and anti-SRP
What is the significance of a high creatine kinase (CK) level in myositis?
Diagnostic for muscle inflammation, often 10x the normal limit
Which antibodies are characteristically associated with dermatomyositis?
Anti Mi-2 and ANA (more common)
What is the antibody associated with the extra-muscular features of dermatomyositis?
anti-Jo1
Which antibodies are characteristically associated with polymyositis?
anti-Jo1
What are the features of polymyositis?
Diffuse proximal muscle weakness.
Second-line investigation for polymyositis and dermatomyositis?
Autoantibodies:
= Myositis specific - Anti-Jo-1, anti-SRP
= Non-specific - ANA, anti-RNP
2nd line test after muscle biopsy
MRI
Dermatomyositis causes the same muscular symptoms as in polymyositis, but also causes characteristic rashes to develop, most notably what?
- Gottron’s papules
- Heliotrope rash
A 43-year-old female presents with a 3-week history of worsening weakness in her upper arms and legs. As a result, she struggles to stand up from a chair and brush her hair. However, she still has good fine motor skills in her hands. Examination reveals bilateral proximal (hip and shoulder girdle) muscle weakness. She denies skin changes but does report some muscle aches over the same period.
Given the likely diagnosis, which of the following tests is unlikely to be significantly raised?
Alkaline phosphatase (ALP)
A 57-year-old woman presents with fatigue and worsening shoulder weakness. She has noticed a slight change in her voice over time and feels it is hoarser. She reports muscle and joint aches and an occasional fever. Due to breathlessness, she has taken sick leave and can no longer complete her daily runs. She has been taking vitamin D supplements, suspecting deficiency as the cause of her symptoms.
On examination, she has roughened skin on her knuckles and elbows, a red rash on her eyes, and puffiness. Blood tests show elevated lactate dehydrogenase, AST, ALT, and creatine kinase. EMG and muscle biopsy confirm the diagnosis.
Given the likely diagnosis, what is the most important complication to be screened for?
Underlying malignancy
A 50-year-old woman presents to the GP feeling weak. She describes difficulty getting up when sitting on a chair and struggles with steps and lifting objects. She hasn’t had any pain, fever, or weight loss. Her medical history is insignificant; the only medication she takes is a multivitamin.
On examination, you note power 4/5 in proximal muscle groups. She has no skin changes. Given the most likely diagnosis, which test would you order for first line?
Creatine kinase (CK)
Which investigation would reveal the diagnosis for those with polymyositis and dermatomyositis?
Muscle biopsy
A 50-year-old man presents with gradually worsening symmetrical muscle weakness, predominantly in the proximal limbs, and a recent increase in creatine kinase levels.
Given the most likely diagnosis, what clinical features is most likely to also be present?
Interstitial lung disease
What are the cutaneous features of dermatomyositis?
(1) Gottron’s papules
= red papules on the dorsal aspect of the finger joints
(2) Shawl rash
= erythema across the upper back and shoulders
(3) Nailfold erythema
(4) Heliotrope rash
= a purple rash on the eyelids
(5) bilateral proximal muscle weakness
What are the lesions found on the finger joints of an individual with dermatomyositis known as?
Gottron’s papules
Which myopathy is associated with underlying malignancy?
Dermatomyositis
What is the rash found on the eyes of people with dermatomyositis known as?
Heliotrope rash
Anti-Mi-2 antibodies are specific for what disease?
Dermatomyositis
