ICD-10 Code G73.3 – Myasthenic syndromes in other diseases classified elsewhere (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G73.3 – Myasthenic syndromes in other diseases classified elsewhere
What it is
Use this code for myasthenic syndromes caused by another underlying disease. It identifies neuromuscular weakness linked to a separate condition, not primary myasthenia gravis.
Clinical signs
Clinical features vary; refer to documentation. Typical findings include fatigable weakness, ptosis, diplopia, and other signs of impaired neuromuscular transmission associated with the underlying disorder.
When to use this code
Assign G73.3 when the record states a myasthenic syndrome is secondary to another disease and the link is documented. Use it when the provider names the associated condition and does not describe primary myasthenia gravis.
Check documentation if the chart only says weakness or neuromuscular symptoms without a clear causal diagnosis. Code the underlying disease separately when instructed by the record and applicable coding rules.
Do not use for
Do not use this code for primary myasthenia gravis or for nonspecific muscle weakness. If the syndrome is not documented as secondary to another disease, check documentation.
Coding tip
Always capture the causative disease first, then add G73.3 only when the provider clearly documents a myasthenic syndrome due to another condition.