Autoimmune process drives SPSD
Autoimmunity, even if not detected by serologic studies, is believed to inhibit expression of gamma aminobutyric acid (GABA) receptors, which, in turn, results in stiffness and spasms. Although what are known as “Dalakas criteria,” proposed in 2009,2 describe the “classic” SPSD phenotype, encompassing roughly three-quarters of SPSD patients, there have now been other phenotypes proposed under SPSD, including isolated forms (stiff limb or trunk syndrome) and “nonclassic” phenotypes like SPS-plus (classic features plus brain stem and/or cerebellar involvement),3 overlap syndromes (for example, classic features with refractory epilepsy/limbic encephalitis), and probably the most severe phenotype, progressive encephalomyelitis with rigidity and myoclonus.
Early and aggressive therapy with benzodiazepines and other GABA-ergic agonists, as well as immune-based treatments, is considered critical to slowing progression of SPSD. However, the insidious onset of what is often a cluster of vague, nonspecific symptoms is a challenge for clinicians to recognize.
Dr. Marinos C. Dalakas
“When a patient comes in with muscular spasms, with stiffness in the back, in the legs, and it’s unexplained and it’s not due to spinal cord disease, or multiple sclerosis ... think SPSD,” said Dr. Dalakas. “Check antibodies – that’s the first thing to do.”
Antibody positivity is most helpful at high levels, he added; low titers can be present in autoimmune diabetes and other conditions, as previously mentioned. The real challenge? When a patient is seronegative.
Embarking on a diagnostic odyssey
Patients “bounce from one clinician to the next looking for answers,” said Dr. Newsome. “Patients will often start with their general practitioner and be referred to physical therapy, rheumatology, or orthopedics, and other specialists, which could include neurology and/or psychiatry, among others. SPSD is often not considered as a possible diagnosis until the patient develops more concrete symptoms and/or objective signs on exam. Of course, considering this diagnosis starts at knowing that it exists.”
Task-specific phobias and exaggerated acoustic startle or sensory reflex are specific symptoms that can red-flag some SPSD patients, said Dr. Dalakas. “Impaired GABA is also important for fears and anxiety. So, when you have a reduction of GABA you have more phobic neuroses – fear of crossing the street, fear of speaking in public, and they get very tense and they cannot perform.
“If the GABA-ergic pathways are dysfunctional, then there’s a relative hyper-excitability within the nervous system,” said Dr. Newsome. “This can be evaluated with electromyography. “The muscles are unhinged and going crazy: Agonists and antagonists are contracting together, which is abnormal. We will also assess for continuous motor unit potential activity within individual muscles – angry muscles just continuously firing. In our experience, this finding appears to be a pretty specific sign of SPS, especially in the torso.” Importantly, the sudden contraction of muscles along with stiffness can lead to traumatic falls, causing major orthopedic and brain injury.
In early stages of SPSD, a careful history and clinical exam is critical to try to shorten what Dr. Newsome calls the patient’s “diagnostic odyssey.”
“It behooves the clinician to put their hands on the patient. Check their back, their abdomen – try to feel for rigidity, paraspinal muscle spasms, and tightness. These regions of the body often have a ropey feel to them, which is due to chronic muscle spasms and tightness. Most [SPSD] patients will have this present in the thoracolumbar area,” he explained. “Check for hyperlordosis, as this is a hallmark sign on exam in SPSD. Additionally, patients can have rigidity and spasticity in their legs or arms. Also, patients with nonclassical phenotypes can present with a variety of other symptoms and findings on exam, including ataxia, nystagmus, ophthalmoparesis, and dysarthria.”
Lumbar puncture can sometimes reveal signs of inflammation, such as an elevated white blood cell count and oligoclonal bands in spinal fluid.
“The classic teaching was that you can only see such findings in conditions like multiple sclerosis, but that’s not the case,” said Dr. Newsome. “You can see these findings in other autoimmune conditions, including SPSD. Hence, as part of the workup, we will have patients undergo lumbar punctures to assess for these markers of autoimmunity.”
Other mimics of SPSD, including multiple sclerosis, tumors, and spinal stenosis, should be ruled out with MRI of the brain and spine.