Persistent hyperplasia of thymus

This code describes a condition where the thymus gland, an organ in the chest involved in immune system development, remains abnormally large beyond infancy or early childhood. This persistence can be identified radiographically or pathologically and is often asymptomatic, but can sometimes be associated with other conditions.

Use this code when documentation explicitly states "persistent hyperplasia of thymus" or "thymic hyperplasia" in an older child or adult. It is often an incidental finding on imaging studies (e.g., CT scan of the chest) performed for other reasons. This diagnosis requires physician documentation of the persistent nature of the hyperplasia.

• Do not confuse with normal thymic size in infants or young children, as thymic involution typically occurs with age.
• Ensure documentation specifies "persistent" to differentiate from transient or reactive thymic hyperplasia, which may resolve.
• Code any associated symptoms or underlying conditions (e.g., myasthenia gravis, Graves' disease) separately as primary or secondary diagnoses, depending on the clinical scenario.