Myasthenia Gravis and Lambert Eaton

Myasthenia gravis

Myasthenia gravis (literally "serious muscle-weakness") is a neuromuscular disease leading to fluctuating muscle weakness and fatiguability. It is an autoimmune disorder, in which weakness is caused by circulating antibodies that block acetylcholine receptors at the post-synaptic neuromuscular junction, inhibiting the stimulative effect of the neurotransmitter acetylcholine. Myasthenia is treated medically with cholinesterase inhibitors or immunosuppressants, and, in selected cases, thymectomy. At 200–400 cases per million it is one of the less common autoimmune disorders.

Signs and symptoms

Ptosis of the left eye.

The hallmark of myasthenia gravis is fatiguability. Muscles become progressively weaker during periods of activity and improve after periods of rest. Muscles that control eye and eyelid movement, facial expression, chewing, talking, and swallowing are especially susceptible. The muscles that control breathing and neck and limb movements can also be affected. Often the physical examination is within normal limits.^[3]

The onset of the disorder can be sudden. Often symptoms are intermittent. The diagnosis of myasthenia gravis may be delayed if the symptoms are subtle or variable.

In most cases, the first noticeable symptom is weakness of the eye muscles. In others, difficulty in swallowing and slurred speech may be the first signs. The degree of muscle weakness involved in MG varies greatly among patients, ranging from a localized form, limited to eye muscles (ocular myasthenia), to a severe or generalized form in which many muscles - sometimes including those that control breathing - are affected. Symptoms, which vary in type and severity, may include asymmetrical ptosis (a drooping of one or both eyelids), diplopia (double vision) due to weakness of the muscles that control eye movements, unstable or waddling gait, weakness in arms, hands, fingers, legs, and neck, a change in facial expression, dysphagia (difficulty in swallowing), shortness of breath and dysarthria (impaired speech, often nasal due to weakness of the velar muscles).

In myasthenic crisis a paralysis of the respiratory muscles occurs, necessitating assisted ventilation to sustain life. In patients whose respiratory muscles are already weak, crises may be triggered by infection, fever, an adverse reaction to medication, or emotional stress.^[4] Since the heart muscle is stimulated differently, it is never affected by MG.

Diagnosis

Myasthenia can be a difficult diagnosis, as the symptoms can be subtle and hard to distinguish from both normal variants and other neurological disorders. A thorough physical examination can reveal easy fatiguability, with the weakness improving after rest and worsening again on repeat of the exertion testing. Applying ice to weak muscle groups characteristically leads to improvement in strength of those muscles. Additional tests are often performed, as mentioned below. Furthermore, a good response to medication can also be considered a sign of autoimmune pathology.

Physical examination

Muscle fatigability can be tested for many muscles.A thorough investigation includes:

• looking upward and sidewards for 30 seconds: ptosis and diplopia.
• looking at the feet while lying on the back for 60 seconds
• keeping the arms stretched forward for 60 seconds
• 10 deep knee bends
• walking 30 steps on both the toes and the heels
• 5 situps, lying down and sitting up completely
• "Peek sign": after complete initial apposition of the lid margins, they quickly (within 30 seconds) start to separate and the sclera starts to show

Blood tests

If the diagnosis is suspected, serology can be performed in a blood test to identify certain antibodies:

• One test is for antibodies against the acetylcholine receptor. The test has a reasonable sensitivity of 80–96%, but in MG limited to the eye muscles (ocular myasthenia) the test may be negative in up to 50% of the cases.

• A proportion of the patients without antibodies against the acetylcholine receptor have antibodies against the MuSK protein.

• In specific situations (decreased reflexes which increase on facilitation, co-existing autonomic features, suspected presence of neoplasm, especially of the lung, presence of increment or facilitation on repetitive EMG testing) testing is performed for Lambert-Eaton syndrome, in which other antibodies (against a voltage-gated calcium channel) can be found.

electromyography, which is considered to be the most sensitive (although not the most specific) test for MG

Edrophonium test

Tensilon test

Imaging

A chest CT-scan showing a thymoma (red circle).

A chest X-ray is frequently performed; it may point towards alternative diagnoses (e.g. Lambert-Eaton due to a lung tumor) and comorbidity. It may also identify widening of the mediastinum suggestive of thymoma, but computed tomography (CT) or magnetic resonance imaging (MRI) are more sensitive ways to identify thymomas, and are generally done for this reason.

Pulmonary function test

Restrictive pattern on spirometry

Associations

Myasthenia Gravis is associated with various autoimmune diseases, including:

• Thyroid diseases, including Hashimoto's thyroiditis and Graves' disease
• Diabetes mellitus type 1
• Rheumatoid arthritis
• Lupus, and
• Demyelinating CNS diseases

Computer Eye Strain: Tips to relieve

Computer Eye Strain: 10 Steps for Relief

1. Get a computer eye exam.

2. Use proper lighting.

3. Minimize glare.

4. Upgrade your display.

5. Adjust the brightness and contrast of your computer screen

6. Blink more often.

7. Exercise your eyes.

8. Take frequent breaks.

9. Modify your workstation.

10. Consider computer eyewear.

Contact Dermatitis

Contact dermatitis is a localized rash or irritation of the skin caused by contact with a foreign substance. Only the superficial regions of the skin are affected in contact dermatitis. Inflammation of the affected tissue is present in the epidermis (the outermost layer of skin) and the outer dermis (the layer beneath the epidermis).Unlike contact urticaria, in which a rash appears within minutes of exposure and fades a

way within minutes to hours, contact dermatitis takes days to fade away. Even then, contact dermatitis fades only if the skin no longer comes in contact with the allergen or irritant. Contact dermatitis results in large, burning, and itchy rashes, and these can take anywhere from several days to weeks to heal. Chronic contact dermatitis can develop when the removal of the offending agent no longer provides expected relief.

Causes

In North/South America, the most common causes of allergic contact dermatitis are plants of the Toxicodendron genus: poison ivy, poison oak, and poison sumac. Specific plant species that can induce

such contact dermatitis include Western Poison Oak, a widespread plant in the western USA. Common causes of irritant contact dermatitis are harsh (highly alkaline) soaps, detergents, and cleaning products.

Types of contact dermatitis

There are three types of contact dermatitis: irritant contact, allergic contact, and photocontact dermatitis. Photocontact dermatitis is divided into two categories: phototoxic and photoallergic.

Chemical irritant contact dermatitis

Physical irritant contact dermatitis

Low humidity

Plants

Allergic contact dermatitis


Common allergens implicated include the following:

• Nickel (nickel sulfate hexahydrate) - metal frequently encountered in jewelry and clasps or buttons on clothing
• Gold (gold sodium thiosulfate) - precious metal often found in jewelry
• Balsam of Peru (Myroxylon pereirae) - a fragrance used in perfumes and skin lotions, derived from tree resin (see also Tolu balsam)
• Thimerosal - a mercury compound used in local antiseptics and in vaccines
• Neomycin - a topical antibiotic common in first aid creams and ointments, cosmetics, deodorant, soap and pet food. Found by itself, or in Polysporin or Triple Antibiotic
• Fragrance mix - a group of the eight most common fragrance allergens found in foods, cosmetic products, insecticides, antiseptics, soaps, perfumes and dental products ^[15]
• Formaldehyde - a preservative with multiple uses, e.g., in paper products, paints, medications, household cleaners, cosmetic products and fabric finishes
• Cobalt chloride - metal found in medical products; hair dye; antiperspirant; metal-plated objects such as snaps, buttons or tools; and in cobalt blue pigment
• Bacitracin - a topical antibiotic found by itself, or as Polysporin or Triple Antibiotic
• Quaternium-15 - preservative in cosmetic products (self-tanners, shampoo, nail polish, sunscreen) and in industrial products (polishes, paints and waxes).^[16]
• Colophony (Rosin) - Rosin, sap or sawdust typically from spruce or fir trees
• Topical steroid - see steroid allergy

Photocontact Dermatitis

Sometimes termed "photoaggravated"(Bourke et al. 2001)^[17], and divided into two categories, phototoxic and photoallergic, PCD is the eczematous condition which is triggered by an interaction between an otherwise unharmful or less harmful substance on the skin and ultraviolet light (320-400 nm UVA) (ESCD 2006), therefore manifesting itself only in regions where the sufferer has been exposed to such rays. Without the presence of these rays, the photosensitiser is not harmful. For this reason, this form of contact dermatitis is usually associated only with areas of skin which are left uncovered by clothing. The mechanism of action varies from toxin to toxin, but is usually due to the production of a photoproduct. Toxins which are associated with PCD include the psoralens. Psoralens are in fact used therapeutically for the treatment of psoriasis, eczema and vitiligo.

Photocontact dermatitis is another condition where the distinction between forms of contact dermatitis is not clear cut. Immunological mechanisms can also play a part, causing a response similar to ACD.

Symptoms

Allergic dermatitis is usually confined to the area where the trigger actually touched the skin, whereas irritant dermatitis may be more widespread on the skin. Symptoms of both forms include the following:

• Red rash. This is the usual reaction. The rash appears immediately in irritant contact dermatitis; in allergic contact dermatitis, the rash sometimes does not appear until 24–72 hours after exposure to the allergen.
• Blisters or wheals. Blisters, wheals (welts), and urticaria (hives) often form in a pattern where skin was directly exposed to the allergen or irritant.
• Itchy, burning skin. Irritant contact dermatitis tends to be more painful than itchy, while allergic contact dermatitis often itches.

While either form of contact dermatitis can affect any part of the body, irritant contact dermatitis often affects the hands, which have been exposed by resting in or dipping into a container (sink, pail, tub, Sun, Swimming Pools With High chlorine ), containing the irritant.

Treatment

Self-care at Home

• Immediately after exposure to a known allergen or irritant, wash with soap and cool water to remove or inactivate most of the offending substance.

- Weak acid solutions [lemon juice, vinegar] can be used to counteract the effects of dermatitis contracted by exposure to basic irritants [phenol etc.].

• If blistering develops, cold moist compresses applied for 30 minutes 3 times a day can offer relief.
• Calamine lotion and cool colloidal oatmeal baths may relieve itching.
• Oral antihistamines such as diphenhydramine (Benadryl, Ben-Allergin) can also relieve itching.
• For mild cases that cover a relatively small area, hydrocortisone cream in nonprescription strength may be sufficient.
• Avoid scratching, as this can cause secondary infections.
• A barrier cream such as those containing zinc oxide (e.g. Desitin, etc.) may help to protect the skin and retain moisture.

Medical Care

If the rash does not improve or continues to spread after 2-3 of days of self-care, or if the itching and/or pain is severe, the patient should contact a dermatologist or other physician or physician assistant. Medical treatment usually consists of lotions, creams, or oral medications.

• Corticosteroids. A corticosteroid medication similar to hydrocortisone may be prescribed to combat inflammation in a localized area. This medication may be applied to your skin as a cream or ointment. If the reaction covers a relatively large portion of the skin or is severe, a corticosteroid in pill or injection form may be prescribed.
• Antihistamines. Prescription antihistamines may be given if nonprescription strengths are inadequate.

Prevention

Since contact dermatitis relies on an irritant or an allergen to initiate the reaction, it is important for the patient to identify the responsible agent and avoid it. This can be accomplished by having patch tests, a method commonly known as allergy testing. The patient must know where the irritant or allergen is found to be able to avoid it. It is important to also note that chemicals sometimes have several different names.^[18]

In an industrial setting the employer has a duty of care to the individual worker to provide the correct level of safety equipment to mitigate the exposure to harmful irritants. This can take the form of protective clothing, gloves or barrier cream depending on the working environment.