Coding Clinic Raises Questions About Uncertain Behavior

The American Hospital Association (AHA) Coding Clinic for the third quarter of 2023 was recently published. There was a question regarding post-molar pregnancy gestational trophoblastic disease/gestational trophoblastic neoplasia (GTD/GTN).

The provider’s final diagnoses were Stage III GTN, multiple bilateral metastatic nodules of the lung, adnexal mass, and presumed vaginal lesion. The questioner noted that “malignant hydatidiform mole” codes to D39.2, Neoplasm of uncertain behavior of placenta. They wanted to know if this was appropriate, if the patient has metastases.

The answer was to code C54.8, Malignant neoplasm of overlapping sites of corpus uteri, and the individual metastatic sites. Their reasoning was that since the malignant GTD/GTN had metastasized, neoplasm of uncertain behavior is not appropriate, and the malignant neoplasm code should be used instead.

This advice perplexes me.

First, let’s address what neoplasm of “unspecified behavior” means; it was not used in this case, but is another point of confusion. This phrase means that no one specified whether the neoplasm was benign or malignant. That information may have been available and not documented, or it may not be available yet. If a provider documents “neoplasm” or “tumor,” the coder picks up unspecified behavior. It can’t be ascertained whether it is a benign or malignant variety if it isn’t documented. The coder uses the table of neoplasms to get the site-specific code. Not applicable here, obviously.

Uncertain behavior, on the other hand, is specifying.

There are two scenarios in which this classification fits. The first is when the pathologist is stymied as to whether a particular tumor has benign or malignant characteristics. They have scrutinized tissue under their microscope, and they are just unsure what the morphology is indicating. The pathologist will include in the report, “of uncertain behavior.”

The other situation represents a specific type of pathology that has the potential to become malignant, but it can’t be predicted whether this patient’s lesion will transform. These conditions often have the word “borderline” in them. Lymphomatoid granulomatosis, borderline ovarian mucinous tumor, and follicular thyroid tumor of uncertain malignant potential are deemed neoplasms of uncertain behavior. These are often alternatively referred to as tumors of uncertain malignant potential. In ICD-11, the titles state “of uncertain or unknown behaviour.”

Let’s discuss this particular scenario. A hydatidiform mole develops in the uterus, but originates from gestational tissue, cells that would normally produce the placenta. It is also called a molar pregnancy. There is rapid and often abnormal cell growth. Most cases of gestational trophoblastic disease are benign, but there is the possibility of it progressing to malignancy. There are four main types of cancer (GTN) that can result from GTD, but let’s focus on only two of them. Invasive or malignant hydatidiform moles (also known as chorioadenoma destruens) are cancerous, but do not usually spread outside of the uterus. The most aggressive form of GTN is choriocarcinoma, which does often metastasize.

It is a little perplexing why a condition which is known to be malignant (that is, malignant hydatidiform mole) is categorized by ICD-10-CM as a neoplasm of uncertain behavior, but it is. Coding Clinic’s point was that once the GTN spread beyond the genital organs, it is no longer considered uncertain behavior. It has declared itself. They are asserting that the category is not strictly based on the morphology.

Their coding advice is incorrect, however. The involvement of the uterus is by spread of the cancer into the muscle layers, but the malignancy arose from placental trophoblastic cells. It is a placenta-originating cancer, not a myometrial or uterine one. The correct code for this patient would be C58, Malignant neoplasm of placenta, not C54.8, Malignant neoplasm of overlapping sites of corpus uteri.

Moving on, there were a couple other important Coding Clinic features in this issue I would like to bring to your attention.

They rectified the lapse of crosswalking HFimpEF (Heart Failure with improved Ejection Fraction), which arose when they addressed HFrecEF (Heart Failure with recovered Ejection Fraction). HFimpEF may now be coded as diastolic heart failure.

Medicinal cannabis use does not code to an F12 code, indicating mental or behavioral disorders due to psychoactive substance use. It is captured as Z79.899, Other long-term (current) drug therapy. This is similar to opioids; prescribed narcotics are not coded in F but as Z79.891, Long-term (current) use of opiate analgesic.

As always, I recommend you read the Coding Clinic issue yourself. There may be other clinical scenarios that relate to your practice. If you are still left with a question, pose it to them (https://www.codingclinicadvisor.com/submit-question) and let them resolve it.