Docetaxel associated myositis.

Introducti̇on: Docetaxel is a microtubule inhibitor in the taxane group and it is a semisynthetic analogue of paclitaxel. It binds to β-tubulin subunits with high affinity, preventing the depolymerization of microtubules during metaphase. Myalgia has been frequently described as a docetaxel-related side effect. However, myositis is a rare side effect of docetaxel.

Case report: A 64-year-old female patient with a right breast mass was diagnosed with invasive breast cancer. The tumor was 100% and 60% positive for estrogen and progesterone receptor, respectively and human epidermal growth factor receptor 2 (HER-2) was positive. There was not any distant metastasis in screening. It was clinically staged as T4N0M0 (stage 3B). Treatment was started with neoadjuvant chemotherapy (CT) as docetaxel plus trastuzumab (TR) plus pertuzumab. The patient applied to the outpatient clinic with muscle pain and weakness which started a few days after the second CT cycle.

Management & outcome: The neurological physical exam was normal except that the muscle strength was 1/5 in the lower extremities with tense swelling. Joint pain or skin lesions were absent. Laboratory results revealed creatine kinase (CK) 4389 U/L. The patient was hospitalized with the diagnosis of myositis/myopathy due to these findings. Autoimmune markers were in normal range. The lower extremity magnetic resonance imaging (MRI) showed intense edema. The patient underwent a muscle biopsy. These findings were compatible with drug-associated necrotizing myopathy.

Di̇scussi̇on: Docetaxel-related myositis is a rare complication and clinicians should be aware of this adverse event in patients with suspicious symptoms and with comorbidities.