American Academy of Professional Coders (AAPC) Practice Exam

Onchitis refers specifically to the inflammation of the nail matrix, which is the tissue located under the base of the nail. This condition can lead to symptoms such as pain, redness, and swelling around the nail. The nail matrix is critical for the production of new nail cells, and any inflammation in this area can affect nail health and growth.

The other options describe different conditions: the infection of the scalp refers to a separate skin issue, thinning of hair involves hair follicles and is unrelated to the nails, and growth of abnormal nails can involve various types of nail disorders, but does not specifically denote inflammation of the nail matrix itself. Thus, identifying onchitis as inflammation of the nail matrix is accurate, aligning with medical terminology in dermatology and pathology.