Some SMA Patients Unable to Walk Unassisted May Have Trouble Chewing

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by Patricia Inacio PhD |

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Difficulties with biting and fatigue while chewing are common among patients with type 2 and type 3 spinal muscular atrophy (SMA) who are unable to walk unassisted, a Dutch study reports.

The findings highlight the need for interventions to help maintain muscle strength in the jaw of these patients in an effort to ease the symptoms.

The study, “Mastication in Patients with Spinal Muscular Atrophy Types 2 and 3 is Characterized by Abnormal Efficiency, Reduced Endurance, and Fatigue,” was published in the journal Dysphagia.

SMA is a genetic disease characterized by the progressive loss of motor neurons, nerve cells that control muscle movement, leading to muscle weakness and shrinkage (atrophy).

Muscle twitches affecting the tongue and jaw are common symptoms among SMA patients, but fewer studies have analyzed more complex bulbar functions, such as mastication (biting and chewing). Bulbar muscles are those that control speech, swallowing, and chewing.

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In the study, a team led by researchers at the University Medical Center Utrecht, in the Netherlands, evaluated the prevalence of self-reported chewing problems in patients with SMA with some form of bulbar dysfunction.

The study enrolled a total of 27 patients, ages 13 to 67, included in the Dutch SMA registry. Of the participants, 18 had type 2 and nine had type 3 SMA. All patients with type 2 SMA and six with type 3, a total of 24, were unable to move without aid (non-ambulatory).

Mastication was assessed by self-reported questionnaires, along with clinical evaluation of the muscles used while chewing. This was evaluated via X-ray-based video and ultrasound. Additional tests included the test of mastication and swallowing solids (TOMASS) and the 6-minute mastication test (6MMT). The exams were conducted by two experienced speech and language therapists.

In the TOMASS test, patients had to eat a standard cracker as quickly as possible, but at a safe pace, during which a video captured the number of bites, chewing, and the time to eat the cracker. The TOMASS test outcomes were reported as a z-score, where scores below 1.5 were considered normal.

In the 6MMT, patients chewed continuously on a chewing tube for a total of six minutes, and a video captured their chewing movements. After the test, and again within five minutes of its completion, the patient’s view of fatigue and pain was assessed using a visual analogue scale (VAS). Scores range from zero to 10, with higher scores indicating more severe fatigue.

All the 24 non-ambulatory patients reported difficulties with mastication — 71% said they had problems with “biting off hard food,” 67% had difficulties with chewing, and 71% reported fatigue while chewing.

The majority (88%) ate food by transforming it to a puree or cutting it to small pieces. More than half (54%) of the patients took 30 minutes or more to finish their meals. Eight patients (33%) had muscle pain, cramps, or tiredness in the jaws when eating.

None of these symptoms were reported by the three patients who were able to walk (ambulatory). One ambulatory patient reported fatigue while chewing.

According to the TOMASS scores, while non-ambulatory patients performed the same number of discrete bites as that of healthy individuals (median z-score of 0.4), they required a higher number of chews (median z-score 1.8), swallows (median z-score 4.3), and time to finish the cracker (median z-score 3.4).

Efficiency of mastication in non-ambulatory patients were similar, regardless of SMA type.

The performance of the three ambulatory SMA patients was similar to healthy individuals.

In the 6MMT, five non-ambulatory patients (21%) could not finish the test due to excessive fatigue of the chewing muscles.

Patients reported significantly more fatigue and pain immediately after and within five minutes of the 6MMT. The median VAS score for fatigue of non-ambulatory patients was 7 immediately after the test and 2.5 within five minutes of completion.

Patients’ reduced ability to open their mouth was found to be associated with mastication problems.

Ultrasound of the chewing muscles showed an abnormal muscle structure in 90% of SMA patients, both ambulatory and non-ambulatory.

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Overall, these findings suggest chewing problems in patients with type 2 and type 3 SMA, particularly those who lost their ability to walk independently, “are characterized by inefficiency, reduced endurance, and fatigue, probably caused by masticatory muscle changes that can be detected by ultrasound,” the researchers wrote.

“Interventions should aim to maintain jaw mobility, dental occlusion [how teeth line up with each other as the jaw opens and closes], and endurance of mastication,” the study concluded.