The SMA medical abbreviation most often means spinal muscular atrophy, an inherited disease that weakens muscles, but it is just as common in imaging and surgery for the superior mesenteric artery, a major blood vessel to the intestines. In liver clinics it can also mean smooth muscle antibody, a blood test.
So the setting matters. A pediatric neurology note or a genetic test result points to the disease, a CT scan of the abdomen points to the artery, and a list of autoimmune liver tests points to the antibody. This page explains each meaning, plus a few close lookalikes such as SMAS.
At a glance
Stands for
Spinal muscular atrophyOther meanings
Superior mesenteric artery; smooth muscle antibodyOlder lab use
SMA-7 or SMA-12, older names for chemistry panelsLookalike
SMAS, superficial musculoaponeurotic systemUsed in
Neurology, genetics, radiology, surgery, hepatologyDo not confuse with
ALS, a different motor neuron disease
Spinal muscular atrophy explained
Spinal muscular atrophy is a genetic condition that damages the lower motor neurons, which sit in the spinal cord and send signals out to the muscles. Without enough of a protein made by the SMN1 gene, these cells are lost and muscles weaken and shrink. It is inherited in an autosomal recessive way, which means a child usually inherits a changed gene from each parent.
SMA is grouped into types by when symptoms start and the highest motor skill reached. Type 1 begins in early infancy and is the most severe form; types 2 and 3 begin later in childhood; type 4 begins in adulthood and is mild. Treatments approved in recent years include nusinersen, risdiplam and onasemnogene abeparvovec, a gene therapy. Many US states now include SMA in newborn screening so treatment can start early.
The superior mesenteric artery in scans and surgery
The superior mesenteric artery branches off the aorta in the upper abdomen and carries blood to most of the small intestine and part of the large intestine. Radiologists mention it on nearly every CT angiogram of the abdomen. Notes may describe narrowing, a blood clot or a tear in the vessel wall.
Imaging report: "CTA abdomen: celiac and SMA widely patent, no dissection." The two main arteries to the gut are open with no tear in their walls, so blood flow to the intestines looks normal on this CT angiogram.
Related problems include mesenteric ischemia, where the bowel does not get enough blood, and SMA syndrome, a rare condition in which the artery presses on part of the small intestine and causes blockage symptoms.
Smooth muscle antibody as a lab test
In hepatology, SMA or ASMA is anti smooth muscle antibody. It is one of the blood tests used when doctors are looking into autoimmune hepatitis, where the body's defenses turn against liver tissue. A positive result is a clue, not a diagnosis on its own, and it is read together with liver enzymes, other antibodies and sometimes a liver biopsy. The result may be reported as a titer, such as 1:80. Labs set their own cutoffs. For more lab shorthand, see the lab test abbreviations guide.
Telling each SMA medical abbreviation apart
| Where you see it | Likely meaning |
|---|---|
| Pediatric neurology, genetics, physical therapy | Spinal muscular atrophy |
| CT, ultrasound or vascular surgery notes | Superior mesenteric artery |
| Liver antibody panel | Smooth muscle antibody |
| Older lab requisitions with a number | Chemistry panel, as in SMA-7 |
The plural form SMAS can mean more than one artery, but in plastic surgery SMAS is its own term, the superficial musculoaponeurotic system, a layer of tissue in the face that surgeons lift during some facelift procedures. Context keeps these separate.
Clinical signs that accompany spinal muscular atrophy
Neurologic exams in SMA often note low muscle tone, weakness that is greater in the trunk and upper legs than in the hands and feet, and absent or reduced deep tendon reflexes. Thinking and learning are not affected by the disease itself. Care usually involves a team including neurology, physical and occupational therapy, breathing and feeding specialists, and genetics. Unlike ALS, which usually begins in adulthood and affects both upper and lower motor neurons, SMA is genetic and affects lower motor neurons.
Where to go from here
If you found SMA on a family member's record and the meaning is unclear, look at the department behind the entry and at the neighboring words. Other letter clashes like this one are collected on the diagnosis abbreviations page.
Meanings here are general. For questions about a specific test result, scan finding or diagnosis, start with the clinician who ordered it, or a genetic counselor for inherited conditions.
Frequently asked questions
What does SMA mean in medical terms?
SMA most often means spinal muscular atrophy, an inherited disease that weakens muscles. In imaging it usually means the superior mesenteric artery, and in liver testing it can mean smooth muscle antibody.
What does SMA mean on a CT scan?
On an abdominal CT or CT angiogram, SMA means the superior mesenteric artery. The report will usually say whether it is patent, meaning open, or narrowed or blocked.
What does SMAS mean in medical notes?
In plastic surgery, SMAS stands for superficial musculoaponeurotic system, a layer of tissue under the skin of the face. In other notes it may simply be the plural of SMA.
Is SMA the same as ALS?
No. Both affect motor neurons, but SMA is an inherited disease usually diagnosed in childhood, while ALS usually begins in adulthood and affects a wider set of motor nerve cells.
What was an SMA-7 test?
SMA-7 was an older name for a basic blood chemistry panel of seven tests, named after the lab machine that ran them. Today most labs call a similar set a basic metabolic panel.