Muscle Weakness Types and Patterns

Types of Weakness

• Primary Weakness: Muscle loses power or cannot perform tasks. Fatigues quickly compared to other muscles. Potential underlying causes include muscle damage, disruptions in nerve signals, and problems with muscle impulses.

• Asthenia: Muscles have normal strength but reduced tolerance. Even minor tasks lead to significant fatigue, and the patient experiences longer recovery times than expected, particularly for exercise and daily activities (ADLs).

• Pseudo Instability: A feeling of joint instability without actual giving way. Occurs when muscles are painful or not firing correctly, often seen in the hip or knee.

Patterns of Weakness

• Spinal/Peripheral Nerve Weakness: Asymmetrical weakness impacting specific muscle groups is common. Reflex changes and corresponding pain/paraesthesia in the affected skin area are often present. Can be caused by inciting events like disc herniation, lateral stenosis, or entrapment.

• Symmetrical Weakness (Limbs): Weakness affecting both limbs, often developing gradually. Possible causes include spinal or vascular system issues, like central stenosis, spinal infection, or peripheral arterial disease (stage 2).

• Proximal Weakness (Shoulder/Hip Girdle): Difficulty with overhead tasks, standing, and stair climbing. Avoidance of these actions may seem like weakness, but underlying causes like dermatomyositis, hyperthyroidism, or polymyalgia rheumatica (often pain-related) may be the issue. Myasthenia gravis can also manifest here, starting from eyes/head and spreading outwards.

• Distal Weakness (Hands/Feet): Subtle changes like reduced finger dexterity, grip strength loss, toe/heel drop are common. This can result from central stenosis, diabetes, vitamin B deficiencies, motor neuron disease, or Guillain-Barre syndrome.

• Middle Cerebral Artery (MCA) Weakness: Upper limb and facial weakness, potentially with spasticity/paralysis. The forehead is typically spared on the face, with numbness/paraesthesia in the corresponding area. Speech issues (Wernicke's aphasia) can accompany these symptoms.

• Anterior Cerebral Artery (ACA) Weakness: Whole leg weakness, typically spastic and accompanied by numbness/paraesthesia. Potential for urinary/bowel issues (incontinence) are possible, along with Broca's aphasia (difficulty expressing speech).

Muscular Dystrophy

• Muscle Dystrophies: A group of inherited disorders that cause progressive muscle weakness and atrophy, due to genetic defects impacting muscle function.

• Duchenne Muscular Dystrophy (DMD): Most common type; affects males (1:3500). Early development may be normal or high-functioning. Shows developmental delays (1-3 years), gait problems, Gower's sign, cognitive issues. Muscle degeneration and necrosis are evident; muscle is replaced by fat (pseudohypertrophy). Usually diagnosed between 3-5 years old; typically wheelchair-bound by 7-13 years old. Reduced lifespan (around 30 years) from cardiopulmonary issues. Elevated serum CPK (creatine phosphokinase) level is a key blood test finding.

• Becker Muscular Dystrophy (BMD): Onset is later and symptoms are milder than DMD. Patients tend to walk longer (into their teens and beyond in some cases) though ambulation challenges are present. Mental impairment is less common. Heart problems are less common but are more severe when present, compared to DMD.

Inflammatory/Endocrine Myopathies

• Inflammatory Myopathies: (covered more thoroughly in CM1) Include conditions like Dermatomyositis, characterized by primary, bilateral proximal muscle weakness, skin rashes (rash on hands/face), and a possible history of breast cancer.

• Endocrine Myopathies: (covered more thoroughly in CM1) Cause chronic and proximal muscle weakness. Muscle weakness can be resolved by addressing the underlying endocrine problem. Possible causes include pituitary disorders (acromegaly), hyperthyroidism, hyperparathyroidism (and resultant osteomalacia), and adrenal issues (Cushing's or Addison's disease).

Motor Neuron Disease (ALS)

• Motor Neuron Disease (ALS): Also known as amyotrophic lateral sclerosis. The most frequent degenerative motor system disease. Characterized by the progressive deterioration of both upper and lower motor neurons, resulting in gradual, painless, widespread weakness. Onset usually in late 50s. Reduced lifespan.

• Symptoms & Signs: Initial signs may involve reduced finger dexterity or intrinsic hand muscle wasting, muscle cramping, stiffness, weakness. Potential for wrist drop, stumbling/tripping, awkward running. Foot drop, and slapping gait patterns can manifest. Speech and swallowing difficulties (bulbar/pseudobulbar features) may also be present. Fasciculations (twitching muscles) are possible, particularly in the tongue and limbs. Muscle atrophy, spasticity, hyperreflexia (or hyporeflexia as both LMN & UMN are involved) are common. Sensory, bowel, bladder, or sexual dysfunction is not expected with ALS. Cognitive impairment may be seen in later stages.

Guillain-Barre Syndrome

• Guillain-Barre Syndrome: An acute immune-mediated demyelinating polyradiculoneuropathy with hallmark progressive weakness over days to weeks, starting from the lower extremities and moving upwards. Usually develops 2-4 weeks after a mild respiratory or gastrointestinal illness. Sometimes, proximal muscle areas (like hip flexion) are first affected. Glove and stocking sensory distribution/pain, and/or aching can occur. Cranial nerve issues (dysphagia, dysarthria, diplopia, pupillary problems, facial droop) are also possible. Respiratory compromise (dyspnea to respiratory failure) is a significant concern. Testing is done with EMG and nerve conduction studies. Immunomodulatory treatment (IVIG and plasma exchange), including supportive ventilation if required, is important.

Bell's Palsy

• Bell's Palsy: Acute facial paralysis (usually unilateral). Peak effect within 48 hours. Possible causes include swelling of the facial nerve, uncertain etiology. Symptoms range from mild numbness to full paralysis, with pain around the ipsilateral mastoid process. Facial nerve palsy is evident (ipsilateral paralysis of the entire face, including the brow), with possible taste/salivation impairment or hyperacusis (clapping response). Reduced tear production is also sometimes observed. Patients experience Bell's Phenomenon – inability to fully close affected eye, and eye rotates up and out) when attempting to close eyes and show teeth. Treatment includes eye protection, high-dose corticosteroids, and antiviral therapy. Recovery is usual (80% spontaneously recovery, but with possible residual facial asymmetry).

Myasthenia Gravis

• Myasthenia Gravis (MG): A rare autoimmune disease that affects acetylcholine receptors at the neuromuscular junction. Results in fatigable muscle weakness, usually starting in the proximal muscles, such as the eyes (ptosis). Weakness can spread to the rest of the body if not managed. Diagnosed by looking for fatigable strength with repeated movements. Eye problems, difficulty in pursuing, pronouncing or pronating movements, and pronator drift are common indications and should be looked into.

This quiz covers various types and patterns of muscle weakness, including primary weakness, asthenia, and pseudo instability. It also explores spinal and peripheral nerve weakness, highlighting their causes and symptoms. Test your understanding of these key concepts in muscle health.