Drug induced myotonia

This diagnosis code signifies a condition characterized by delayed muscle relaxation after voluntary contraction, specifically caused by an adverse reaction to a medication. It represents a form of myotonia that is iatrogenic, meaning it is induced by medical treatment.

Use this code when documentation clearly states that a patient's myotonic symptoms are a direct result of drug exposure. This typically involves a temporal relationship between drug initiation and symptom onset, and often resolution or improvement upon drug discontinuation. Supporting documentation should identify the specific drug implicated.

• Always code the adverse effect of the drug first (T36-T50 with 5th or 6th character 5) followed by this code.
• Do not confuse with congenital myotonia or other inherited myotonic disorders, which have different code assignments.
• Ensure the medical record explicitly links the myotonia to a specific drug; "drug-induced" must be documented.