Kugelberg Welander Spinal Muscular Atrophy

Updated: Sep 01, 2021
  • Author: Joyce L Oleszek, MD; Chief Editor: Stephen Kishner, MD, MHA  more...
  • Print

Practice Essentials

Spinal muscular atrophies (SMAs) represent a rare group of inherited disorders that cause progressive degeneration of the anterior horn cells of the spinal cord. The exact cause of the degeneration is unknown. Loss of these cells results in a progressive lower motor neuron disease that has no sensory involvement and that is manifested as hypotonia, weakness, and progressive paralysis. Kugelberg Welander spinal muscular atrophy (also known as Wohlfart-Kugelberg-Welander syndrome or mild SMA) is a milder form of SMA, with symptoms typically presenting after age 18 months. [1, 2, 3]

SMAs were first described in the 1890s, by Guido Werdnig, a physician from the University of Vienna, in his lecture "On a Case of Muscular Dystrophy with Positive Spinal Cord Findings." Soon after, Professor Johann Hoffmann from Heidelberg University presented a paper describing a syndrome of progressive atrophy, weakness, and death during the early childhood period of siblings with genetically normal parents. Both physicians conducted autopsies on their patients and found severe atrophy of the ventral roots of the spinal cord. They also found histologic evidence of loss of motor neurons in the anterior horn cells of this region. Hoffmann called the syndrome spinale muskelatrophie (spinal muscular atrophy).

In the early 1960s, Byers and Banker classified SMA into categories based on the severity and age of onset of the symptoms, in an effort to predict prognosis. Their system, summarized below, became the basis for the most widely recognized system now used for the classification of SMA.

  • Type I

    • Onset of symptoms before age 6 months

    • Also known as infantile onset SMA, or Werdnig-Hoffmann disease

  • Type II [4]

    • Onset of symptoms at age 6-18 months

    • Also known as chronic SMA, juvenile SMA, or intermediate SMA

  • Type III [4]

    • Onset of symptoms after age 18 months, usually in late childhood or adolescence

    • Also known as Kugelberg Welander SMA, or mild SMA

Although Byers and Banker's classification system focuses on only the above 3 categories, many sources refer to a fourth type of SMA.

  • Type IV

    • This category is reserved for onset of symptoms during early adulthood.

    • This disorder usually carries a much more favorable prognosis than do the other types of SMA.

This article focuses only on SMA types III and IV.

Related Medscape Drugs & Diseases topics:

Focal Muscular Atrophies

Spinal Muscle Atrophy

Spinal Muscular Atrophy

Related Medscape resource:

Resource Center Spinal Disorders

Signs and symptoms of spinal muscular atrophy

Signs and symptoms of SMA include the following:

  • Proximal muscle weakness is seen in SMA, with the pelvic girdle being more affected than the shoulder girdle [5]
  • Patients have decreased muscle tone
  • Patients have diminished deep tendon reflexes; ankle reflexes, however, may be preserved until very late in the disease's progress
  • Fasciculations may be present in the tongue or shoulder girdle muscles (especially after manual muscle testing)
  • Minipolymyoclonus, a fine, irregular tremor of the outstretched fingers, may be seen
  • Calf pseudohypertrophy has occasionally been noted, but muscle wasting of the affected musculature is more prominent
  • Patients may have a positive Gowers sign and a waddling gait
  • Approximately one third of patients have facial and masseter muscle weakness
  • Sensory examination findings are normal

Workup in spinal muscular atrophy

Routine diagnostic testing for SMA involves targeted mutation analysis to detect deletion of exons 7 and 8 of SMN1.

Serum creatine kinase levels may be elevated but usually not to the extent that they are elevated in persons with muscular dystrophy. Serum aldolase levels also are commonly elevated in persons with types III and IV SMA.

Other tests include the following:

  • Muscle biopsy - Reveals evidence of neurogenic atrophy and chronic reinnervation in SMA
  • Electromyography (EMG) and nerve conduction studies (NCS) - Diffuse abnormalities on EMG are seen in the extremities and bulbar musculature

Management of spinal muscular atrophy


Spinal muscular atrophy (SMA) has no known cure; thus, most care for the patient with SMA is focused on symptomatic control and preventative rehabilitation. [6] Maintaining the patient's joint mobility is very important because the goal is to decrease the incidence of contractures. Plantar flexion contractures are the most common.

Ankle-foot orthotics worn at night may help to provide prolonged, passive stretching to prevent worsening of ankle plantar flexion contractures.

Stretching and strength training in patients under the care of an experienced physical therapist are very important components of the preventative rehabilitation approach.

Occupational therapy is useful for teaching the patient ways to increase his/her independence in activities of daily living (ADL).

Patients with SMA may require consultation with a speech therapist if dysphagia is present or diet modification is needed.


If scoliosis develops in a patient with SMA, spinal instrumentation and fusion may be necessary. [7] Some upper extremity function can be lost after fusion.

Tendon lengthenings may be needed to improve joint position.



Spinal muscular atrophy (SMA) is caused by successive motor unit degeneration. Muscle atrophy, caused by a progressive loss of the anterior horn cells in the spinal cord, is universal. The motor nuclei in the lower brainstem, usually those of cranial nerves V-XII (V, VII, IX, XII), also may be involved. Various stages of degeneration can be observed histologically at these sites. As the nerve cells decrease in number, replacement gliosis, pyknosis, and secondary Wallerian degeneration in the roots and peripheral nerves are observed. These processes generally begin at the caudal end of the cord and typically are symmetrical. The lower limbs usually are affected sooner and more profoundly than are the upper limbs. This degeneration most often affects the proximal musculature before it impacts the distal. Note that, unlike in amyotrophic lateral sclerosis (ALS), no corticospinal tract involvement is seen in SMA.

A study by Querin et al involving adult patients with SMA type III or IV found that spinal cord gray matter had considerably atrophied between C2 and C6, while, possibly owing to an adaptive mechanism, the gray matter had grown denser in the motor and extramotor cortical regions. [8]




United States

Spinal muscular atrophy (SMA) has an estimated incidence of 1 case per 15,000 live births. The genetic carrier prevalence is 1:80.


SMA has an estimated incidence of 1 case per 15,000-20,000 live births worldwide.


SMA types III and IV, unlike types I and II, are consistent with survival well into adulthood. [9] Significant morbidity occurs from progressive weakness, and patients may frequently fall or may have difficulty with stairs. Most patients use wheelchair mobility by their fourth decade of life. Scoliosis and joint contractures are also extremely common. Morbidity associated with these conditions often can be minimized with spinal surgery, as well as with aggressive physical therapy. Respiratory failure in SMA types III and IV is not as common as in types I and II. Respiratory complaints usually can be managed medically, and mechanical ventilation seldom is necessary. [10, 11, 12, 13]

Cardiovascular pathologies have frequently been found in cases of SMA. A literature review by Wijngaarde et al reported that among these heart-related comorbidities, cardiac rhythm disorders most often accompanied milder forms of SMA, while structural cardiac disorders (primarily septal defects and cardiac outflow tract abnormalities) were most commonly associated with more severe SMA. [14]

A study by Souza et al of 20 individuals with SMA type IV determined limb-girdle muscle weakness to be the most frequent clinical symptom, being found in 75% of the patients. Fasciculations and absence of tendon reflexes made up the most frequent neurologic findings, occurring in 45% and 90% of patients, respectively. The investigators also found that disease duration correlated with functional scale scores, including those on the Hammersmith Functional Motor Scale Expanded, the Amyotrophic Lateral Sclerosis Functional Rating Scale Revised, the Revised Upper Limb Module, and the Spinal Muscular Atrophy Functional Rating Scale. Such correlation was also reported for the 6-minute walk test and the Timed Up and Go test. [15]


Spinal muscular atrophy (SMA) affects all races equally.


Spinal muscular atrophy affects males and females at the same rate; however, disease progression is more severe in males.


The age of onset for spinal muscular atrophy is discussed above in the Background section.