6.1.2 Approach to Lower Motor Neuron Disease PDF

**OUTLINE** I. **Introduction** II. **History Taking** a. Central Hypotonia vs. Peripheral Hypotonia III. **Neurologic Examination** IV. **Lower Motor Neuron Weakness** V. **Acute Flaccid Paralysis** VI. **Anterior Horn Cell Disorder** a. Poliomyelitis b. Spinal Muscular Atrophy VII....

**OUTLINE** I. **Introduction** II. **History Taking** a. Central Hypotonia vs. Peripheral Hypotonia III. **Neurologic Examination** IV. **Lower Motor Neuron Weakness** V. **Acute Flaccid Paralysis** VI. **Anterior Horn Cell Disorder** a. Poliomyelitis b. Spinal Muscular Atrophy VII. **Diseases of Neuromuscular Junction** VIII. **Diseases of Muscle (Myopathies)** IX. **Summary** X. **Case Synchronous Session** XI. **Appendix** +-----------------------+-----------------------+-----------------------+ | **LEGEND** | | | +=======================+=======================+=======================+ | ⭐ | 🖊️ | 📖 | | | | | | Must | Lecture | Book | | | | | | Know | *\[lec\]* | *\[bk\]* | +-----------------------+-----------------------+-----------------------+ OBJECTIVES {#objectives.ListParagraph.TransOutline} ========== After completing this lecture, you should be able to: 1. Characterize the distinguishing features of the following: - Upper motor neuron vs. Lower motor neuron - Signs and symptoms of central vs. peripheral hypotonia - Distinguishing features of muscle tone vs. muscle weakness 2. Create differential diagnosis for neuromuscular disorder. 3. Discuss the appropriate medical and diagnostic evaluation of diseases of neuromuscular disorder. INTRODUCTION {#introduction.TransOutline} ============ **Figure 1. The Anatomy of Upper and Lower Motor Neuron** - 🖊️The pathway affected in patients with [paralysis] is the [corticospinal tract or the descending pathway]. Lesions involving the **CORTICOSPINAL TRACT** are responsible for what we call **UPPER MOTOR NEURON PARALYSIS**. - The corticospinal tracts end in the anterior horn cell of the spinal cord. This neuron plus the motor roots and the peripheral nerve, innervate the neuromuscular junction and transmit signal to the skeletal muscles, and this consists of what we call LOWER MOTOR NEURONS. - Interruption therefore in the motor pathway at specific level, whether motor pathway from the cortex down to the spinal cord, will determine the type of motor paralysis the patient will present. +-----------------------------------+-----------------------------------+ | **Table 1.** ⭐ **UMN vs. LMN** | | +===================================+===================================+ | **Upper Motor Neuron** | **Lower Motor Neuron** | +-----------------------------------+-----------------------------------+ | Paralysis affect movement rather | Individual muscle or group of | | than muscle **(paresis)** | muscles are affected | | | **(paralysis)** | +-----------------------------------+-----------------------------------+ | Muscle wasting is only from | Wasting pronounced | | disease, therefore slight. | | | Occasionally mark in chronic | | | severe lesion **(disuse)** | | +-----------------------------------+-----------------------------------+ | **Spasticity**/ of clasp knife | **Flaccidity** | | type | | +-----------------------------------+-----------------------------------+ | Muscle **hypertonic** | Muscle **hypotonic/areflexic** | +-----------------------------------+-----------------------------------+ | **(+) Clonus** | (-) Clonus | | | | | **(+) Babinski** | (-) Babinski | +-----------------------------------+-----------------------------------+ - 🖊️Muscle wasting is **not immediately** prominent in patients with UMN lesions especially during the very early stage. HISTORY TAKING {#history-taking.TransOutline} ============== DIFFERENCE BETWEEN CENTRAL vs PERIPHERAL HYPOTONIA {#difference-between-central-vs-peripheral-hypotonia.TransSubtopic1} -------------------------------------------------- - 🖊️Central Hypotonia involves the brain causing hypotonia or weakness while Peripheral hypotonia is from anterior horn cell to the muscle. - History of fetal movement in utero, fetal presentation, increased amount of amniotic fluid (ex: Polyhydramnios), low APGAR score, as well as neurologic examination in phenotypic characteristics are additionally important differentiating factors. - Both central and peripheral hypotonia have problems in respiration but the pathology in peripheral is due to weakness of the intercostal muscle and the diaphragm. +-----------------------------------+-----------------------------------+ | **Table 2.** ⭐ **Central | | | Hypotonia vs. Peripheral | | | Hypotonia** | | +===================================+===================================+ | **Central Hypotonia - UMN** | **Peripheral Hypotonia - LMN** | +-----------------------------------+-----------------------------------+ | Depressed LOC | Alert look | +-----------------------------------+-----------------------------------+ | Seizure | Weak cry and suck (fatigable cry) | +-----------------------------------+-----------------------------------+ | **Hyperactive DTR** | **Areflexia/Hyporeflexia** | +-----------------------------------+-----------------------------------+ | **Hypotonia** | **Fasciculation** | | | | | | 🖊️ obvious in the tongue | +-----------------------------------+-----------------------------------+ | Developmental delay | Weakness with paucity of | | | spontaneous movement | +-----------------------------------+-----------------------------------+ | Dysmorphic features, | Myopathic facies | | microcephaly, MCA | | | | 🖊️ characterized as tented or | | 🖊️ pictures of malformation or | inverted V-shaped lip, long face, | | defect | and high arch palate | +-----------------------------------+-----------------------------------+ | 60-80% of cases | 15-30% of cases | +-----------------------------------+-----------------------------------+ | DDx: | DDx: | | | | | - Cerebral Palsy | - Congenital myopathy | | | | | - Hypoxemic Ischemic | - Congenital myotonic dystrophy | | Encephalopathy | | | | - Spinal Muscular Atrophy | | | | | | - 🖊️Duchenne Muscular dystrophy | +-----------------------------------+-----------------------------------+ | *From 2025 trans:* | | +-----------------------------------+-----------------------------------+ | Normal Creatinine Kinase | Raised (or normal) Creatinine | | | Kinase | +-----------------------------------+-----------------------------------+ | Apnea, irregular respiration | Prolonged breathing difficulties, | | | ventilator dependence | +-----------------------------------+-----------------------------------+ | Multiple congenital abnormalities | History of polyhydramnios | +-----------------------------------+-----------------------------------+ | PERIPHERAL HYPOTONIA | | | | | | - Floppy Infant | | | | | | | | | | | | - "Frog-like posture"; "Rag | | | doll" | | | | | | | | | | | | - Inability to maintain normal | | | posture against gravity | | | | | | - Diminished resistance to | | | passive movements | | | | | | - Excessive range of joint | | | mobility | | | | | | - Principal presenting feature | | | of most NMDs in newborn is | | | hypotonia or floppy infant | | +-----------------------------------+-----------------------------------+ MUSCLE TONE vs MUSCLE STRENGTH {#muscle-tone-vs-muscle-strength.TransSubtopic1} ------------------------------ - 🖊️The decrease or absence in muscle tone is **not** synonymous with weakness. You can be weak but with normal or increased muscle tone. - **Muscle tone** is [tension in a muscle at rest or resistance of muscle to stretch]. Therefore, hypotonia is diminished resistance of muscle to passive stretching while weakness is diminished muscle for power or strength. - **Muscle Strength** is the muscle's [ability to contract and create force in response to resistance]. NEUROLOGIC EXAMINATION {#neurologic-examination.TransOutline} ====================== +-----------------------------------+-----------------------------------+ | **Table 3. Normal Infant vs | | | Hypotonic Infant** | | +===================================+===================================+ | **Resting Position** | | +-----------------------------------+-----------------------------------+ | **Normal** | **Hypotonic** | +-----------------------------------+-----------------------------------+ |  |  | | | | | 🖊️Lying supine with legs flexed | 🖊️**Frog Leg Posture; Rag-Doll | | and arms adducted. | Appearance** | | | | | (2025) | - 🖊️Inability to maintain | | | normal posture against | | - Cerebral Palsy | gravity, diminished | | | resistance to passive | | - Semi-flexed arms, elbows, | movements, and excessive | | hips and knees | range of joint mobility. | | | | | | (2025) | | | | | | - Descended arms and elbows | | | | | | - Jug handle hands (internal | | | rotation) | | | | | | - Reduced spontaneous movement | | | | | | - Legs fully abducted and arms | | | lying beside the body, either | | | extended or flexed | +-----------------------------------+-----------------------------------+ | **Horizontal Suspension** | | +-----------------------------------+-----------------------------------+ | **Normal** | **Hypotonic** | +-----------------------------------+-----------------------------------+ | 🖊️The infant is suspended in |  | | prone position with the | | | examiner's hand underneath the | 🖊️In hypotonic infants, there | | chest | will be [head lag], | | | and legs appear to be limping, | | (2025) | forming an [inverted U | | | posture] | | - Head is lifted when infant is | | | already 2 | (2025) | | | | | - The head should rise, and the | - Rag doll appearance | | hips should flex | | | | - Inverted U-shape | | | | | | - Weakness | | | | | | - Very poor muscle tone on his | | | Paraspinous | | | | | | - Rag doll on ventral or | | | horizontal suspension | | | | | | - Drape over the physician's | | | hands forming a U-shape | +-----------------------------------+-----------------------------------+ | **Vertical Suspension** | | +-----------------------------------+-----------------------------------+ | **Normal** | **Hypotonic** | +-----------------------------------+-----------------------------------+ | 🖊️Arms are adducted, legs are |  | | flexed with upright position of | | | the head and shoulders while | 🖊️Elevation of the shoulders and | | doing the ventral suspension | arms and extension of the legs | | | | | (2025) | Also called **Slip Through | | | Maneuver** | | - Adducts arms when lifted on | | | the armpit | (2025) | | | | | - Legs are flexed and adducted | - Wing their arms due to low | | | tone and slips through the | | | hands | | | | | | - Legs and hips are extended | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **Traction Response** | | +===================================+===================================+ | **Normal** | **Hypotonic** | +-----------------------------------+-----------------------------------+ |  | 🖊️Excessive head lag or | | | hyperextension or absence of | | 🖊️The lift of the head is almost | flexion of the arms and legs are | | parallel to the body. There is | evident when the infant is pulled | | flexion in all limb joint | by the arms from a supine to | | | sitting position, demonstrating | | (2025) | an [abnormal traction | | | response.] | | Few seconds of head flexion | | | | (2025) | | | | | | - Marked head lag on pull to | | | sit maneuver | | | | | | - Infant's head slightly behind | | | the body and then falls | | | forward upon reaching the | | | sitting position | +-----------------------------------+-----------------------------------+ Non-Neurologic Manifestation of Peripheral Hypotonia {#non-neurologic-manifestation-of-peripheral-hypotonia.TransSubtopic1} ---------------------------------------------------- - 🖊️Aside from the clues in neurologic examinations hypotonic patients with LMN disease may present with:  **Figure 3. Myopathic Facies: Inverted V-shaped Lip & Eyelid Lag.**  **Figure 4. Myopathic Facies: Inverted V-shaped Lip & High Arched Palate.**  **Figure 5. Hyperlaxity of the hand, wrist, and finger joints.** **Figure 6. W-position.** - 🖊️Physical finding is indicative of joint hyperlaxity that accompanies hypotonia.  **Figure 7. Ptosis and external ophthalmoplegia in a floppy weak child.** - 🖊️Can be seen in a patient with myasthenia gravis. #### 🖊️Other non-neuromuscular complains such as: {#other-non-neuromuscular-complains-such-as.TransSub-subtopic3} **Figure 8. Pectus excavatum seen in congenital myopathy. Pectus carinatum in spinal muscular atrophy.**  **Figure 9. Toe walking in Duchenne Muscular Dystrophy.** **Figure 10. Leg cramps in Charcot-Marie-Tooth disease.**  **Figure 11. Scoliosis in Duchenne Muscular Dystrophy and Congenital Myopathy.** **Figure 12. Cryptorchidism or undescended testes and joint contracture in Congenital Myopathy.**  **Figure 13. Arthrogryposis or Fused Joint in decreased fetal movement in utero seen in Spinal Muscular Atrophy Type 0.** **Figure 14. Cardiomegaly in patient with Pompe\'s disease**  **Figure 15. Tongue Fasciculations** **(Lec Vid at 8:18 min)** **Figure 16. Muscle Fasciculations** **(Lec Vid at 8:18 min)**  **Figure 17. Percussion myotonia in Myotonic Dystrophy** **(Lec Vid at 8:28 min)** - 🖊️Myotonia is a [very slow relaxation of muscle after contraction], regardless of whether that contraction was [voluntary or was induced by a stretch reflex or electric stimulation]. - This is a percussion myotonia in myotonic dystrophy. Observe for a very slow relaxation of muscle after contraction. **Figure 18. Tongue Myotonia** **(Lec Vid at 8:28 min)** 1. **LOWER MOTOR NEURON WEAKNESS** **Figure 19.** LMN Disorders ⭐ - ⭐Remember the **keywords** in this table when reviewing, these are the different **anatomic** **localizations** and **etiologic** **diagnosis** for LMN disease. A. **DIFFERENTIAL LOCALIZATION OF DISEASES PRODUCING HYPOTONIA** **Figure 20.** Different Localizations ⭐ - 🖊️We must clearly [define the distribution and pattern of weakness], then examine the **Deep Tendon Reflexes (DTRs)**. - If [weakness] is quite [marked or generalized and associated with the absence of reflexes], think of **ANTERIOR HORN CELL** pathology, which we will confirm with **fasciculations** and **neurogenic EMG**. - To distinguish a **Peripheral** **Nerve** lesion from a **Muscle** lesion, it is crucial to determine the **pattern of weakness**: - **Proximal** vs. **Distal**. As a rule: - **Myopathies** (Muscle): **Proximal** weakness - **Neuropathies** (Peripheral Nerve): **Distal** weakness - **Exception**: Myotonic Dystrophy (DM1), where there is **Distal** weakness. - **Neuromuscular Junction (NMJ) Lesions**: - [Prominent fluctuating weakness,] particularly [facial weakness], such as **ptosis**, which may be the only manifestation of **Myasthenia Gravis** in children. - *\[Batch \'24\] **CK Levels**:* - [CK is markedly elevated] in Viral Myositis, Pompe Disease, and Duchenne Muscular Dystrophy. - It is [normal or slightly elevated] in Hypophosphatasia (HPP) and Myotonic Dystrophy, though we typically do not test CK in HPP. I. **ACUTE FLACCID PARALYSIS (AFP)** A. **DOH DEFINITION** - 🖊️A clinical syndrome consisting of **rapid onset (acute) weakness** that in some cases may involve the **respiratory** and **bulbar** muscles - Causes are **varied**, ranging from **infection** to **trauma,** **vascular** **lesions**, **tumor**, **GBS**, **demyelinating** disorder, **HPP**, etc. - What is the importance of the program of DOH? This is to **identify** and **monitor AFP** cases due to **poliomyelitis** so that appropriate and timely public health measures can be taken to meet the WHO AFP surveillance performance indicator target for polio-free countries. B. **CASE DEFINITION** - 🖊️Acute Flaccid Paralysis (AFP): - **Acute**: Refers to a sudden onset of paralysis, typically occurring **within 3 to 4 days**, but **may extend up to 2 weeks**. - **Flaccid**: Indicates a **loss of muscle tone** in the **affected** **limbs** or **body part**, resulting in a **floppy appearance**. - **Paralysis**: Refers to the **reduction** or **loss** **of the ability to move** the affected limb(s). - Criteria for AFP: - **Children \