And the winner is...ICD-10!

Cracking the Code

Alexander Miller

Dr. Miller, who is in private practice in Yorba Linda, California, represents the American Academy of Dermatology on the AMA-CPT Advisory Committee.

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ICD-9: comfort, stability, stagnation. Then, wham! Change. It always happens, either slowly, or stealthily, or suddenly. Just ask the dinosaurs.

So here we are, with ICD-10 upon us. Unlike an asteroid, which slammed suddenly, obliterating an unsuspecting stable dinosaur society, it has been like a steadily approaching ship full of invaders, identifiable from afar, detouring at times, but inexorably coming closer, all the while declaring its intentions. ICD-10’s purpose is clear, but what are the details?

ICD-10 has two basic features that fully distinguish it from ICD-9. First, the coding sequence is totally different, being fully alphanumeric (a letter followed with numbers). Second, it provides greater descriptive and diagnostic precision than ICD-9. Examples of similarities and distinguishing differences follow.

As readily seen from a perusal of the ICD-9 to ICD-10 Crosswalk for Dermatology, available at, many of the ICD-10 codes directly correspond to those in ICD-9, and simply entail choosing a different identifying code. However, there are classes of entities that reveal substantially new or greater coding specificity. Such specificity must be extractable from the medical record and expressed in the ICD-10 coding. You may think that since your electronic health records system defines ICD coding based upon the medical record, coding will automatically take care of itself. Well, yes, coding may get done, but whether it is precise and appropriate will still be the biller’s (and ultimately the provider’s) responsibility. An understanding of the coding will enable providers and billers to ferret out the most appropriate codes.

Knowing the logic within ICD-10 will instantly help one to steer to the optimal alphanumeric coding sequence. The initial letter of a code refers to a general category of conditions and the ICD-10 chapters that describe them. Below are the principal letters and chapters pertaining to dermatology:


In general, appropriate ICD-10 codes consist of a letter followed by two numbers, a decimal, and then at least one other number. Only a few entities are fully specified by three characters. Examples are scabies (B86) and HIV disease (B20). [pagebreak]

Although Medicare has announced that for the first year of ICD-10 implementation any code from a valid code set will be billable and payable, there are two major caveats. First, if a list of four or more character codes follows the “category” code listing, then only the more descriptive codes are billable. Example: ICD-10 code C00 heads a category of codes for malignant neoplasm of the lip, C00.0 C00.9. If one were to bill Medicare with code C00, the claim would be rejected. However, codes C00.0 C00.9 are likely to be payable by Medicare during the course of one year starting from Oct. 1, 2015. Simple concept: if a three character ICD-10 code heads a series of related codes that include a decimal point, choose one of these latter codes for billing. Second caveat: a pertinent Medicare National Coverage Determination (NCD) or Local Coverage Determination (LCD) document will list applicable and payable ICD-10 codes. In such instances coverage and payment will apply only to the listed codes. Read further Medicare clarifying information.

Do you feel that the above is complicated? Make it simple: code to the highest level of specificity from the get-go. That will satisfy both short and long-term Medicare and private insurer coding requirements.

There are some diagnostic details that simply do not exist in ICD-9.

The following table delineates ICD-10 entities that are either absent or not detailed in ICD-9, and are likely to be used in your practice.


Example 1: You excise an epidermal inclusion cyst from the right back and code the diagnosis with ICD-10 L72.3, “sebaceous cyst.”

Answer: Correct. ICD-10 lists two codes appropriate for an epidermal inclusion (epidermoid) cyst. The first is “epidermal cyst,” L72.0, and the second is “sebaceous cyst,” L72.3. The two terms are commonly used interchangeably by medical professionals and in insurance company coverage guidelines. Dermatologists recognize that epidermoid cysts do not generate sebaceous material. Consequently, a stickler for nomenclature may choose to use L72.0 for epidermal inclusion cysts and L72.3 for solitary sebaceous cysts, such as a single steatocyst. More crucial to reimbursement is whether an insurer recognizes both or one of the codes for claims adjudication purposes. [pagebreak]

Example 2: A patient has an extensive dermatitis. You generate a differential diagnosis of contact allergy, a systemic drug allergy, or an autoimmune process. As you are unsure of the diagnosis, you code ICD-10 L30.9, “dermatitis, unspecified.”

Answer: Correct, as the chart does not describe any dermatitis category. A related code is: L30.8, “other specified dermatitis”. One may choose this code when the record describes a particular category of dermatitis, such as a papulosquamous, an eczematous, or morbilliform dermatitis.

Example 3: You diagnose a contact allergic dermatitis to a topical facial care preparation, but are unsure of the exact causative agent. Seeing the uncertainty in the chart record, your biller codes with ICD-10 L23.5, “allergic contact dermatitis to other chemical products.”

Answer: Incorrect. Although the dermatitis constitutes an allergic reaction to a chemical, the patient record indicates that the allergy is to a cosmetic. Consequently, the most precise coding is L23.2, “allergic contact dermatitis due to cosmetics.” ICD-10 distinguishes between allergic and irritant contact dermatitides, and also provides codes for specific causes of contact dermatitis, including drugs, adhesives, chemicals, food, plants, solar radiation, and cosmetics. Within most of these categories there is a code for “unspecified dermatitis.” This latter code may be used when the record indicates an uncertainty as to whether the dermatitis is of an allergic or irritant contact nature, such as L25.0, “unspecified contact dermatitis due to cosmetics.”

Example 4: A biopsy of a pigmented lesion on the face indicates a lentigo maligna. As this is a melanoma, your biller submits ICD-10 code C43.39, “malignant melanoma of other parts of face.”

Answer: Incorrect. The ICD-10 distinguishes between invasive and in-situ melanomas. As a lentigo maligna is an in-situ variety of melanoma, the precise code is D03.39, “melanoma in-situ of other parts of face.”

Example 5: You biopsy a peculiar nevus on the chest. The biopsy reveals a junctional nevus with moderate to focally severe atypia. This nevus is benign, but such nevi have a potential of evolving into a melanoma. Do you select a benign ICD-10 code, D22.5, “melanocytic nevi of trunk,” based upon the non-malignant state of the nevus at the time of its biopsy, or should you choose D48.5, “neoplasm of uncertain behavior of skin,” since the nevoidal atypia implies a future malignant potential?

Answer: Incorrect. There is no perfect answer to this conundrum. The nevomelanocytic lesion’s future behavior, if unchecked, is uncertain: it could remain benign but atypical, or it could progress to a melanoma. In practice, one would fully remove such a lesion, as its future behavior is uncertain and unpredictable. Consequently, one is justified in preferring ICD-10 diagnosis D48.5, “neoplasm of uncertain behavior of skin.”