Pocket Medicine: The Massachusetts General Hospital Handbook of Internal Medicine (119 page)

• Limb weakness proximal > distal; DTRs preserved; minimal/no atrophy

• Exacerbations triggered by stressors such as URI, surgery, pregnancy or postpartum, meds (eg, aminoglycosides, procainamide, phenytoin); prednisone can
worsen
acutely

• Myasthenic crisis = exacerbation → need for respiratory assistance

• Cholinergic crisis = weakness due to
overtreatment
with anticholinesterase medications; may have excessive salivation, abdominal cramping and diarrhea; rare at normal doses

Diagnostic studies

• Bedside: ptosis at baseline or after >30 sec of sustained upgaze, improved with ice pack over eyes for 2–5 min, Se 77%, Sp 98%

• Neostigmine test: temporary ↑ strength; false
&
occur; premedicate w/ atropine

• EMG: ↓ response with repetitive nerve stimulation (vs. ↑ response in Lambert-Eaton)

• Anti-AChR Ab: Se 80%, 50% if ocular disease only; Sp >90%; muscle specific receptor tyrosine kinase (MuSK) Ab account for most AchR Ab
cases

• CT or MRI of thorax to evaluate thymus (65% hyperplasia, 10% thymoma)

Treatment

• Thymectomy if thymoma; may lead to improvement in up to 85% Pts w/o thymoma

• Cholinesterase inhibitors (eg, pyridostigmine) are most rapid acting (benefit in 30–60 min)

• Immunosuppression: prednisone (benefit in wks) ± azathioprine, cyclophosphamide (benefit in 6–12 mo)

• Myasthenic crisis: treat precipitant

consider d/c anticholinesterase if suspect cholinergic crisis

immunosuppression with glucocorticoids (in monitored setting as risk for initial worsening)

IVIg or plasmapheresis of equal efficacy (
Ann Neurol
2010;68:797)

ICU if rapid or severe (follow FVC, NIF)

MYOPATHIES

Etiologies

• Hereditary: Duchenne, Becker, limb-girdle, myotonic, metabolic, mitochondrial • Endocrine: hypothyroidism, hyperparathyroidism, Cushing syndrome • Toxic: statins, fibrates, glucocorticoids (incl. critical illness myopathy), zidovudine, alcohol, cocaine, antimalarials, colchicine, penicillamine • Infectious: HIV, HTLV-1, trichinosis, toxoplasmosis

• Inflammatory (see “Rheumatology”): polymyositis, dermatomyositis, inclusion body myositis
Clinical manifestations

• Progressive or episodic weakness (not fatigue)

• Weakness most often symmetric, proximal > distal (stairs, rising from sitting, etc.) • ± Myalgias (though not prominent or frequent), cramps, myotonia (impaired relaxation) • May develop either pseudohypertrophy (dystrophies) or mild muscle atrophy • Assoc. organ dysfxn: cardiac (arrhythmia, CHF), pulmonary (ILD), dysmorphic features
Diagnostic studies

• CK, aldolase, LDH, electrolytes, ALT/AST, PTH, TSH, ESR, HIV

• Autoantibodies (anti-Jo1, antisynthetase, anti-Mi-2, anti-SRP, ANA, RF) • EMG/NCS: low-amplitude, polyphasic units with early recruitment, ± fibrillation potentials • Muscle biopsy, molecular genetic testing (where indicated)

HEADACHE

Primary headache syndromes (International Headache Society Classification)

•
Tension-type
: constant pressure, freq bilateral; a/w myofascial sensitivity in neck or head

Triggers: stress, sleep deprivation, dehydration, hunger

Treatment: OTC analgesics (NSAIDs, acetaminophen; risk of med overuse HA!) for episodic; TCAs for chronic

•
Cluster HA
and trigeminal autonomic cephalgias (TACs)

Characterized by unilateral rhinorrhea, red/tearing eye, miosis/ptosis, lid edema, sweating, differentiated by timing

Cluster:
>
, unilateral eye pain, attacks 15 min–3 h, worsened by EtOH. Ppx: CCB (verapamil). Rx: high-flow O
₂
, sumatriptan IN/SC, lidocaine IN.

Paroxysmal hemicrania:
similar to cluster, but
>
, attacks 2–45 min. Rx: indomethacin.

Hemicrania continua:
>
, icepick-like pain lasting >3 mo. Rx: indomethacin.

Short-lasting unilateral neuralgiform HA w/ conjunctival injection and tearing
(SUNCT)
:
>
, excruciating, stabbing, electrical pain, 5 sec–6 min, up to 200×/d. Rx: lamotrigine, gabapentin, topiramate.