Man with SMA type 4 shows rare fake muscle enlargement in calf: Report
Case highlights need for genetic testing to achieve correct diagnosis
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- In what's believed to be the first such case, SMA type 4 presented in a man, 51, with a false enlarged calf muscle and progressive weakness.
- This rare case highlights the critical need for genetic testing for accurate diagnosis, according to the researchers.
- Early identification and diagnosis are crucial for timely treatment and slowing disease progression in SMA regardless of type.
The case of a 51-year-old man ultimately diagnosed with spinal muscular atrophy (SMA) type 4 is believed to mark the first time this form of the rare genetic disease has had as its main symptom a false enlargement of the large muscle on the back of the lower leg.
In a new report, researchers in China described a man who had a false enlargement, or pseudohypertrophy, of the gastrocnemius muscle in the calf. Pseudohypertrophy occurs when a muscle is enlarged due to fat or other tissue buildup, but it’s actually weaker than normal muscle.
The man, who also had progressive weakness in all four limbs and numbness in the forearms and hands, was eventually diagnosed with SMA type 4 via genetic testing, the team noted.
“SMA presenting with pseudohypertrophy of the gastrocnemius muscle and near-complete loss of motor function is extremely rare and has not been previously reported,” the team wrote.
According to the researchers, “this rare case highlights that pseudohypertrophy of the gastrocnemius muscle may be a rare manifestation of type [4] spinal muscular atrophy, and clinical differential diagnosis should be made with [muscular dystrophy] and other diseases.”
The case was described in “A type IV spinal muscular atrophy with gastrocnemius pseudohypertrophy caused by SMN1 deletion: a case report and literature review,” which was published in the journal BMC Neurology.
SMA is typically caused by mutations in the SMN1 gene that lead to low levels of the SMN protein. This results in the progressive loss of motor neurons, the nerve cells that control movement, leading to symptoms such as muscle weakness and wasting.
SMA type 4 is a rare and relatively mild form of the disease in which symptoms develop in adulthood, much later than in other SMA types. This disease type generally does not impact life expectancy and rarely affects the respiratory muscles.
Man sought treatment after muscle weakness worsened
Here, researchers from The First Affiliated Hospital of Anhui University of Chinese Medicine in Hefei described the case of a man who had experienced progressive muscle weakness for more than 16 years. He sought treatment after that weakness worsened over the prior two months.
His muscle weakness had started in the legs and gradually worsened, also affecting his arms. The recent worsening of symptoms had affected the man’s ability to care for himself and walk.
Previous hospital examinations identified herniated disks — problems in the rubbery cushions that sit between the bones of the spine — in the neck region, while electromyography testing suggested lesions in the spinal cord. His preliminary diagnosis, before being treated at the researchers’ hospital, was muscular dystrophy, a group of diseases that also cause muscle weakness.
Subsequent physical examinations indicated the man had decreased strength in the hands and legs. He also was found to have the pseudohypertrophy of the gastrocnemius muscle and a positive Gower sign, which indicates weakness in the lower body.
Genetic analysis revealed the man had a mutation in both SMN1 copies, which led to a diagnosis of type 4 SMA.
A thorough medical history should be obtained, relevant examinations should be conducted, and genetic testing should be performed when necessary. … The goal is to achieve early identification, diagnosis, and treatment to slow disease progression and reduce the burden on patients and their families.
Disease-modifying treatment for SMA was recommended, but the patient refused. He later underwent spinal surgery, but his symptoms continued to worsen and the prognosis was poor.
The team noted that “SMA presents with a wide range of clinical phenotypes and is often misdiagnosed or overlooked in clinical practice.”
As such, “a thorough medical history should be obtained, relevant examinations should be conducted, and genetic testing should be performed when necessary,” the researchers wrote, noting that “the goal is to achieve early identification, diagnosis, and treatment to slow disease progression and reduce the burden on patients and their families.”
