39
Table 5. Musculoskeletal Toxicities
5.2 Myositis
Workup/Evaluation
• Complete rheumatologic and neurologic history regarding differential diagnosis and
rheumatologic and neurologic examination including muscle strength, and examination
of the skin for findings suggestive of dermatomyositis. Muscle weakness is more typical
of myositis than pain. Consider pre-existing conditions that can cause similar symptoms.
• Blood testing to evaluate muscle inflammation; CK and aldolase. Transaminases
(AST, ALT) and lactate dehydrogenase (LDH) can also be elevated.
• Troponin to evaluate myocardial involvement. Other cardiac testing such as ECG and
echocardiogram or cardiac MRI (see CV section for further details).
• Autoantibody testing to evaluate possible concomitant myasthenia gravis (anti-
acetylcholine receptor (AChR) and anti-striational antibodies)
• Inflammatory markers (ESR and CRP).
• Consider electromyography (EMG), imaging (MRI) and/or biopsy on an individual
basis when diagnosis is uncertain and overlap with neurologic syndromes such as
myasthenia gravis is suspected.
• Consider paraneoplastic autoantibody testing for myositis (e.g., anti-TIF1-γ, anti-
NXP2, and other myositis autoantibodies as indicated), especially if patient had
muscle-related manifestations before receiving ICPi.
• Urinalysis for rhabdomyolysis.
Monitoring: CK, ESR, CRP, Aldolase if CK has not been elevated
G1: Complete examination and laboratory work-up as above.
G2: Complete history and examination as above; autoimmune myositis blood panel;
EMG, MRI imaging of affected joints
Early referral to a rheumatologist or neurologist.
G3–4: As for Grade 2
Urgent referral to a rheumatologist or neurologist.
Grading Management of Myositis alone*
G1: Mild weakness with or
without pain.
• Continue ICPi.
• If CK and/or aldolase are elevated and patient has
muscle weakness may offer oral corticosteroids,
starting prednisone at 0.5 mg/kg/day. Offer
analgesia with acetaminophen or NSAIDs for
myalgia if there are no contraindications.
• Consider holding statins.
(cont'd)
