What is Congenital Smooth Muscle Hamartoma?
Congenital smooth muscle hamartoma is a non-harmful overgrowth of mature smooth muscle, first identified by Sourreil in 1969. It can develop from the various muscle groups in the body like the muscle attached to hair follicles, the muscle in the scrotum, and even the muscle in the nipples. Most often, it appears in the lower back area (lumbosacral area). It usually shows up as an isolated occurrence. Importantly, this muscle overgrowth doesn’t transform into cancer, so in most situations, no treatment is needed.
What Causes Congenital Smooth Muscle Hamartoma?
Congenital smooth muscle hamartoma, a rare skin condition, is believed to occur from unusual development of a particular muscle (arrector pili) during the early growth phase in the womb, especially during the formation of the middle layer of the embryo or mesoderm. It is speculated that hypertrichosis, or excessive hair growth, might happen due to the stimulatory effect of certain cells (CD34 positive dermal dendritic cells) residing in the hamartoma on the layer of skin where hair follicle stems are located.
This skin condition tends to occur spontaneously with no clear pattern. However, some recent reports of it occurring in families indicate that there might be a genetic factor at play.
Very rarely, a widespread form of this condition can occur, leading to folds in the skin. This has been noted as a symptom of a rare condition known as Michelin tire baby syndrome, and might accompany other bodily symptoms or conditions.
Risk Factors and Frequency for Congenital Smooth Muscle Hamartoma
Congenital smooth cell hamartoma, a rare condition, occurs in about 1 in 2600 live births. When we look at who it affects, it’s slightly more common in males according to existing literature.
Signs and Symptoms of Congenital Smooth Muscle Hamartoma
Congenital smooth muscle hamartoma is a condition that is often present from birth, but might not be diagnosed until early infancy. It usually doesn’t cause symptoms, but in some cases, it can cause itching, pain, or numbness. This condition can occur in various parts of the body including the area near the lower back, trunk and upper limbs, but it has also been found in less common places like the scalp, eyelids, nipples, scrotum, and foot. The size of this condition can vary, with it sometimes reaching up to 10 centimeters.
There are three main types of congenital smooth muscle hamartoma that are clinically recognized:
- The classic form, which appears as a defined, skin-colored or pigmented plaque that has dense overlying hair growth.
- The papulo-follicular form, which is less common and shows up as large patches with multiple small, round, skin-colored bumps surrounding hair follicles. These can merge to form irregularly-shaped plaques.
- The mixed form, which includes features of both the classic and papulo-follicular forms.
Besides these forms, there can be various, less common presentations, like linear atrophic plaques, small bumpy plaques, or red patches with irregular boundaries and slight sinking of the tissue underneath.
With time, congenital smooth muscle hamartoma tends to grow in size, in line with the child’s growth, while the increased pigmentation and hair growth often decrease. This condition typically presents as a single lesion, although multiple lesions have been reported in rare cases.
A unique feature of congenital smooth muscle hamartoma is the positive pseudo-Darier sign – rubbing the skin leading to temporary hair erection, redness, and hardening of the skin, caused by the contraction of the smooth muscle cells of the hamartoma. However, this sign is only seen in half of all cases. Sometimes rubbing the skin can also lead to worm-like movements on the surface of the lesion.
Testing for Congenital Smooth Muscle Hamartoma
For diagnosing a congenital smooth muscle hamartoma, no special tests are needed.
However, some experts use a non-invasive tool called a dermoscope to study the hair density of the hamartoma. According to some reports, the number of hairs on the hamartoma is linked to the number of smooth muscle bundles it contains.
Treatment Options for Congenital Smooth Muscle Hamartoma
Congenital smooth cell hamartoma, a benign skin growth, doesn’t pose a risk of becoming cancerous. As such, treatment isn’t necessary unless someone wants to improve their appearance.
One possible treatment is surgical removal, which can be done in various places like the scrotum with great outcomes. However, when the growths are on the face or are very large, reconstruction can be difficult and complex. So, it’s worth looking into other treatment alternatives.
Laser therapy might be a good option to consider. If there’s excessive hair growth on the growth, hair removal laser can be used. For congenital smooth muscle hamartomas that show up as a red skin patch, a pulsed dye laser can help lessen the redness. This type of laser works by getting rid of blood vessels and doesn’t directly affect the growth.
What else can Congenital Smooth Muscle Hamartoma be?
For the most part, a smooth cell hamartoma (which is a type of birthmark) is diagnosed by a doctor simply by looking at it. Sometimes, however, a laboratory test on a tissue sample (histopathological examination) may be needed to rule out similar conditions.
One condition that is quite similar is Becker hamartoma, which typically develops around puberty. This condition usually shows up as a clear, defined patch of skin that may be darker and thicker than the surrounding skin. Both conditions can look similar under a microscope too, as they can both show increased numbers of smooth muscle cells in the skin. However, unlike smooth cell hamartoma, Becker hamartomas tend to get darker and thicker over time. Because of these similarities, some experts think that they may actually be variations of the same condition.
Smooth cell hamartoma might also be confused with a few other skin conditions like birthmarks from melanocytic nevus (a type of mole), piloleiomyoma (a growth made up of smooth muscle cells), café-au-lait spots (light-brown skin spots), and nevus pilosus (a type of hairy mole). Again, lab testing of a tissue sample can be quite helpful in getting an accurate diagnosis. Importantly, it’s crucial to distinguish smooth cell hamartoma from a melanocytic nevus, because the latter can sometimes turn into skin cancer.
Piloleiomyoma also looks a lot like smooth cell hamartoma under a microscope. If the muscle cells and connective tissue are not as distinct as they usually are, doctors should consider piloleiomyoma.
Finally, it can sometimes be tricky to tell apart a smooth cell hamartoma that was missed at birth from one that developed later on. Certain features, like slight darkening of the skin, less dense hair, and a lack of response to touch (known as negative pseudo-Darier sign), could suggest that the hamartoma appeared later, rather than being present from birth.
