Secondary
EM
| Essential thrombocythemia | Myeloproliferative disorder (MPD):
Most significant cause of secondary EM (≤25% of affected persons) EM is frequently the presenting complaint & may precede diagnosis of MPD by several yrs. Ingestion of a single dose of aspirin relieves pain for up to several days. (SCN9A-EM & other secondary causes of EM do not have the same dramatic response).
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| Polycythemia vera or thrombotic thrombocytopenic purpura | |
| Rheumatologic disorders | Gout & autoimmune disorders incl systemic lupus erythematosus, rheumatoid arthritis, & vasculitis |
| Paraneoplastic syndrome | Rare cause of secondary EM |
| Medication | e.g., verapamil, nifedipine, bromocriptine, & ticlopidine Potentially reversible cause of secondary EM
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| Environmental toxins |
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Neuropathies
| Diabetes mellitus Alcoholism HIV infection Lyme disease
| These conditions may cause burning pain similar to EM but are much less likely to be assoc w/redness, warmth, heat intolerance, or relief w/cooling. |
Other
conditions
| Reflex sympathetic dystrophy | A complex regional pain syndrome that may be indistinguishable from SCN9A-EM in early stages but is much more likely to be unilateral Usually follows injury in affected limb (e.g., wrist fracture) & evolves to incl signs such as ↓ circulation May also be assoc w/changes in nails, joints, & bone density
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| Peripheral vascular disease | May be assoc w/pain of distal extremities triggered by exercise (claudication); w/chronic disease, may cause change in skin color Assoc w/smoking & cardiovascular or cerebrovascular disease
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| Raynaud's phenomenon | Vasospasm, pain, & skin color changes Typically exacerbated by exposure to cold (unlike SCN9A-EM)
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Fabry disease
| Burning pain of distal extremities in childhood Differentiated from SCN9A-EM by XL inheritance & other clinical features (e.g., angiokeratomas, characteristic corneal & lenticular opacities, & ↑ occurrence of reno- & cerebrovascular disease)
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Other genetic
causes of
neuropathic
pain
| TRPA1 familial episodic pain syndrome | AD inheritance (OMIM 615040). Episodes of upper-body pain beginning in infancy triggered by fasting, cold, fatigue, & exercise, accompanied by altered breathing, sweating, tachycardia & followed by exhaustion |
| SCN10A familial episodic pain syndrome | AD inheritance (OMIM 615551). Burning, intense itch, hyperalgesia or pain in distal extremities reported in middle-aged adults |
| SCN11A familial episodic pain syndrome | AD inheritance (OMIM 615552). Numbness, tingling, & pain of the hands & feet accompanied by autonomic features (e.g., hyperhidrosis, diarrhea, & palpitations) |
