Common PNS Neurology Disorders: "Weakness"
Sections
The following are some common, important neurological conditions that cause weakness. However, numerous other neurological and non-neurological causes of weakness.
Overview
Myopathy
Polymyositis & Dermatomyositis (Inflammatory Myopathies)
Arthropathy
Neuromuscle Junction Disorder
Neuropathy (& Neuronopathy)
Guillain-Barre Syndrome (Acute Inflammatory Demyelinating Polyneuropathy)
Motor Neuron Disease
Amyotrophic Lateral Sclerosis (ALS) (aka Lou Gehrig's disease)
Disease Specifics
Inflammatory Myopathies
Polymyositis & Dermatomyositis are inflammatory (aka autoimmune) myopathies. They produce myositis, which manifests with a limb-girdle pattern of weakness.
Shoulder girdle weakness: Patients struggle to raise their arms above their head, for instance to comb their hair.
Pelvic girdle weakness: Patients struggle to stand from a chair or climb stairs.
Skin changes: Heliotrope eyelid rash refers to inflammation of the face that manifests blue-violet (or violaceous) color (like a lilac, hence: heliotrope), of the eyelids.
- Butterfly-shaped, malar erythematous rash.
- Shawl sign: an erythematous, photosensitive rash across shoulder, neck, and back of the head.
- Gottron's papules: small, swollen inflammatory lesions of red scaly areas over the knuckles.
- Calcinosis cutis, which is aberrant calcium depositions in the skin and subcutaneous tissues.
Systemic involvement can produce dysphagia from pharyngeal or esophageal involvement; interstitial lung disease (ILD), which manifests with dyspnea; congestive heart failure that can occur from myocarditis; and there is an increased risk of malignancy in inflammatory myopathies (more-so in dermatomyositis than polymyositis).
The creatine kinase (CK or CPK) is characteristically elevated (500 to 10,000k) whereas the ESR is only possibly elevated.
Polymyalgia Rheumatica
Polymyalgia rheumatica (PMR) is roughly 10 – 20 times more common than the inflammatory myopathies ( ~ 1/1,000 vs 1/20,000).
Just like the inflammatory myopathies, most patients are adult women with limb-girdle weakness.
PMR patients are generally slightly older (70 y.o.) than inflammatory myopathies (50 y.o.) and in PMR. It has a higher incidence in whites than in blacks.
Patients develop pain and stiffness rather than frank motor weakness (the weakness is a functional condition), because this is an inflammatory arthropathy NOT a myopathic process.
The CPK should be normal (or relatively normal) and the ESR (erythrocyte sedimentation rate) is elevated (at least > 40) in 85% of cases. Note that other inflammatory markers, including CRP (C reactive protein) are also elevated.
Glucocorticoids (anti-inflammatories) can quickly reduce the arthropathy and unlock the functional weakness.
Myasthenia Gravis
Myasthenia gravis classically causes a fatigable weakness that is worsened with activity and diminished with rest.
MG most often presents with ocular symptoms (~ 75%), most often asymmetric ptosis, which manifests with diplopia or blurred vision (worsened with reading or driving). Fatigable ptosis can be brought-out on physical exam with prolonged upgaze.
Bulbar weakness manifests with dysarthria and dysphagia, trouble swallowing with choking or regurgitating food when eating, and fatigable weakness with chewing. It can lead to respiratory failure.
Generalized weakness presents in the majority of MG patients (even ~50% of the patients who present with isolate ocular involvement will still progress to limb weakness).
Deep tendon reflexes will not be affected.
Late-onset MG patients have a higher likelihood of having thymoma, thus it is critical to get a chest CT to look for an associated thymoma.
Acetylcholine receptor antibodies (binding (most frequently), and also blocking and modulating (less frequently)) are positive in ~ 85% of patients with generalized MG (~ 50% of those with ocular myasthenia).
Guillain-Barre Syndrome
This acute polyneuropathy characteristically presents with ascending numbness and weakness and lower motor neuron findings (eg, muscle cramps).
Campylobacter jejuni, which causes diarrhea, is the most common infectious cause (up to 40% of cases in the US are due to Campylobacter jejuni).
The classic pattern in GBS is symmetric, ascending numbness, followed by severe weakness (often to the point of paralysis) and diminished or absent muscle stretch reflexes over a 2 – 4 week time period.
Autonomic dysfunction (gastric hypomotility, urinary retention, cardiac dysrhythmias, and blood pressure swings) can plague patients with GBS.
Facial weakness and bilateral ptosis represent the oculobulbar palsies that occur in roughly half of GBS cases.
Respiratory failure: Almost one-third of patients will develop phrenic nerve failure with resultant diaphragmatic paralysis and require mechanical ventilation.
Plasmapheresis or IVIG are immunotherapies. Most importantly, management involves monitoring for respiratory failure with frequent respiratory measurements (forced vital capacity and negative inspiratory force).
Cerebrospinal Fluid (CSF) testing is the primary, key helpful diagnostic test; it demonstrates a mildly elevated protein (~ 60) in the setting of a normal WBC (<50), which is called cytoalbuminologic dissociation.
Amyotrophic Lateral Sclerosis
The average age of onset is ~ 55 years old (but it can present at a wide range of ages) and that the average life expectancy from the time of diagnosis is ~ 3 years.
Diagnosis requires clinical evidence of UMN & LMN signs plus EMG evidence of acute and chronic denervation in multiple myotomes (muscle groups innervated by a single spinal nerve) in 3 regions (cervical, thoracic, lumbosacral, or cranial).
UMN Disease: In upper motor neuron disease, there is spastic muscle tone, the reflexes are hyperactive (possibly with clonus), and there are pathologic reflexes (eg the Babinski sign) are present.
LMN Disease: In lower motor neuron disease, there is flaccid muscle tone, the reflexes are hypoactive (or absent), and pathologic reflexes are absent.
The dysarthric pattern of speech in ALS is one of its most recognizable symptoms. There is characteristic preservation of extraocular muscle strength, which helps distinguish ALS from myasthenia gravis wherein asymmetric ptosis is the most common presenting feature.
Focal asymmetric weakness is a common pattern: wrist drop, foot drop, and thigh wasting. Unlike myasthenia gravis and the inflammatory myopathies, ALS typically presents with an asymmetric, focal pattern of weakness and only later becomes confluent.
Respiratory failure from diaphragm denervation is the leading cause of death in ALS.
