Symmetric proximal weakness is most commonly associated with primary muscle disease (myopathy). However, diseases of the neuromuscular junction, neuropathies, spinal cord disease, and very rarely cerebral infarction can produce similar symptoms. Patients with symmetric proximal weakness commonly describe difficulty rising from a chair, climbing stairs, and combing their hair.
Myelopathy and lumbar radiculopathies from spinal canal stenosis typically cause asymmetric weakness; however, unusual presentations of these common conditions do occur. For instance, while rare, symmetric isolated involvement of the L2/L3 nerve roots causes weakness of hip flexion and knee extension along with a reduced or absent patellar reflex. Cervical or thoracic myelopathy with corticospinal tract involvement classically causes a pattern of prominent weakness of hip flexion, knee flexion, and ankle dorsiflexion. If the ankle dorsiflexion weakness is subtle, it may not be appreciated on examination giving the impression of proximal weakness alone. If myelopathy is suspected, magnetic resonance imaging (MRI) of the cervical and thoracic spine should be performed.
Several unique conditions should be considered in patients with isolated symmetric proximal arm weakness. Acute, proximal arm weakness with preservation of hand and leg strength (“man in a barrel” syndrome) may be seen with bilateral cerebral infarctions in the anterior watershed zones, typically as a consequence of hypoperfusion. Brain MRI is diagnostic, and vessel imaging should be performed, as large vessel stenosis is commonly present. Cervical spine syrinx classically causes symmetric bilateral arm or hand weakness, as well as loss of pain and temperature sensation with preservation of vibration sensation in the back and neck in a “cape-like” distribution. MRI of the cervical spine will identify a syrinx; if present, brain MRI should also be performed, as associated Chiari malformations can be present. Cervical myelopathy affecting the upper cervical spinal cord at C5/C6 can cause prominent proximal arm weakness. In this case, upper motor neuron abnormalities (i.e., brisk reflexes) are usually present below the level of injury.
Chronic inflammatory demyelinating polyneuropathy often causes a distinct pattern of distal numbness with proximal weakness. Patients often reports paresthesias and loss of sensation in their feet while at the same time reporting greater difficulty getting out of a chair or going up stairs (see Chapter 90 ).
Serum creatine kinase (CK) is helpful in distinguishing myopathic from non-myopathic disease. However, one should approach modest levels of CK elevation with caution, as this may also be seen in neuropathic or motor neuron disease. In a patient with nonfluctuating, symmetric proximal weakness without numbness and a CK level >1500 U/L, myopathy is the likely cause. In patients with lower CK levels and electromyography (EMG) demonstrating small motor units with early recruitment, myopathy is also the likely diagnosis. In some instances of chronic myopathies, the small motor units expected on EMG may not be present and a more neurogenic pattern may be seen. In these instances, muscle biopsy may be helpful to distinguish these entities (see Chapter 99 ).
Myasthenia gravis (MG) is an autoimmune disorder caused by antibodies directed against the postsynaptic neuromuscular junction of skeletal muscle. MG is characterized by fluctuating weakness that worsens with activity and improves with rest. In generalized MG, weakness may involve the limb muscles, respiratory muscles, pharyngeal muscles, extraocular muscles, and levator palpebrae (see 97 , 98 ).
In a patient with proximal weakness without numbness and diffuse chronic denervation on needle EMG, motor neuron diseases such as amyotrophic lateral sclerosis (ALS), Kennedy disease (spinal-bulbar muscular atrophy), or spinal muscular atrophy are most likely. Symmetric weakness is an uncommon initial presentation of ALS, as it usually begins with asymmetric weakness (see Chapter 96 ).
Lambert-Eaton myasthenic syndrome is an autoimmune disease associated with antibodies against the voltage-gated calcium channel (VGCC). Weakness is commonly seen in the proximal limbs, particularly in the legs, mimicking a myopathic process. Other symptoms include dysarthria, dysphagia, and dysautonomia (e.g., dry mouth or dry eyes). CK levels are usually normal. Diagnosis is based on nerve conduction studies/electromyography and the presence of serum VGCC antibodies (see Chapter 97 ).