Can immunotherapy cause muscle weakness and how to manage it

Yes, immunotherapy can cause muscle weakness in some people, ranging from general fatigue to true muscle inflammation (myositis) or nerve-related problems, though these are less common. ^[1] Fatigue and muscle or joint aches are among the more frequent treatment effects, while immune-related myositis, myasthenia gravis, and neuropathies are rarer but potentially serious and need prompt care. ^{[1] [2]}

What “muscle weakness” may mean on immunotherapy

• General fatigue: feeling very tired or “low energy,” sometimes related to thyroid changes caused by treatment. ^[3]
• Muscle/joint symptoms: new or worsening muscle pain (myalgia), joint pain (arthralgia), stiffness, or limb swelling. ^[4]
• Inflammatory muscle disease (myositis): true weakness, trouble climbing stairs, lifting arms, rising from a chair, or holding your head up; may include swallowing or breathing difficulty. ^[5]
• Nerve or neuromuscular conditions: myasthenia gravis-like weakness, Guillain–Barré, neuropathies; uncommon but serious. ^[6]

Why this matters: most side effects can be managed safely if recognized and treated early; delays can lead to complications. ^[7]

Red flags that need urgent medical attention

• Rapidly worsening weakness, trouble breathing, swallowing, drooping eyelids, or double vision. ^{[5] [6]}
• New severe muscle pain with dark urine or marked weakness (possible significant muscle inflammation). ^[5]
• Severe fatigue with dizziness, headache, or low blood pressure (possible endocrine issues). ^[8]

If these occur, contact your oncology team immediately, and do not take another dose until you’re assessed. ^[8]

Why immunotherapy can cause weakness

Immunotherapy can over-activate the immune system, leading it to inflame normal tissues such as muscle, nerves, thyroid, or other organs. ^[1] This can appear as fatigue from thyroid dysfunction or as immune-related myositis/neuromuscular syndromes that directly reduce muscle strength. ^{[3] [2]}

How clinicians evaluate weakness

• History and exam to distinguish fatigue, pain, and true loss of strength. ^[5]
• Blood tests (e.g., muscle enzymes), thyroid function, and adrenal testing when indicated. ^{[3] [8]}
• Sometimes EMG, MRI of muscles, or muscle biopsy if myositis is suspected. ^[5]

Your team may withhold immunotherapy temporarily while evaluating and treating significant symptoms. ^[8]

Treatment options

• Mild aches or stiffness: acetaminophen or NSAIDs if appropriate; monitor closely. ^[9]
• Suspected moderate–severe immune-related inflammation (e.g., myositis, significant arthritis/arthralgia): corticosteroids are commonly used to calm the immune reaction, with dose and route tailored to severity. ^[9]
• Severe neuromuscular events (e.g., myasthenia gravis, Guillain–Barré, severe myositis): urgent specialist care, immunotherapy is usually held; steroids and other therapies may be needed. ^{[6] [2]}
• Endocrine causes (e.g., thyroid-related fatigue): labs checked; treat the hormone problem and adjust cancer therapy as needed. ^{[3] [8]}

Early reporting allows treatment to start sooner, which generally leads to better outcomes. ^[7]

Practical ways to cope day to day

• Energy management: plan important tasks at your “best” times, use short rest breaks (15–20 minutes), and pace activities. ^[3]
• Gentle activity: light, regular movement can reduce fatigue; avoid pushing into exhaustion and adjust based on daily tolerance. ^[10]
• Rehabilitation support: physical therapists can help build strength and balance safely; occupational therapists can optimize daily tasks and conserve energy. ^[11]
• Hydration and nutrition: stay well hydrated and maintain protein intake to support muscles, as tolerated. ^[12]
• Medication review: ask before using over‑the‑counter pain relievers or supplements; your team can guide safe choices with your regimen. ^[9]
• Symptom diary: track when weakness worsens, activities affected, and any associated symptoms (vision changes, shortness of breath, swallowing trouble). ^[5]

Combining early medical management with tailored rehabilitation often restores function and improves quality of life. ^[11]

When treatment can continue

Your team may resume immunotherapy after symptoms improve and you are stabilized, balancing cancer control with safety. ^[8] Close follow‑up is common to catch any recurrence early. ^[8]

Key takeaways

• Immunotherapy can cause fatigue and muscle/joint aches; less often it can trigger myositis or nerve-related weakness. ^{[1] [2]}
• Report new or worsening weakness quickly especially if it affects breathing, swallowing, or vision so treatment can start early. ^[6]
• Management ranges from rest and simple pain relief to corticosteroids and specialist care, plus rehabilitation to regain strength. ^{[9] [6] [11]}

If you ever feel sudden or severe weakness or difficulty breathing or swallowing, seek urgent medical care right away. ^[6]