Diagnosis of the HSANs depends primarily on clinical examinations and specific sensory and autonomic assessments. Pathologic examinations serve to further confirm differences. In recent years identification of specific genetic mutations for some disorders has aided diagnosis. Replacement or definitive therapies are not available for any of the disorders so that treatment remains supportive and directed toward specific symptoms.
The only diagnostic feature common to all HSAN is the absence of an axon flare following intradermal histamine. [HISTAMINE TESTS- Normal and FD responses]
If there is difficulty distinguishing between the HSAN using clinical signs, then sural nerve biopsy is suggested.
Clinical Feature |
HSAN III FD |
HSAN IV CIPA |
HSAN II CSN |
CAD |
| Histamine test | No axon flare | No axon flare | No axon flare | No axon flare |
| Overflow tears | No | Yes | Delayed | Yes |
| Lingual fungiform Papillae | No | Yes | No | No |
| Deep tendon reflexes | Absent | Present | Absent | Absent |
Sural Nerve Biopsy |
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| Myelinated neurons | Slight decrease | Marked decrease | Severe decrease | Marked decrease |
| Unmyelinated neurons | Severe decrease (25% of normal) | Very severe decrease (5-10% of normal) | Moderate decrease | Slight decrease |
FD: familial dysautonomia, CIPA: Congenital insensitivity to pain with anhidrosis,
CSN: Congenital sensory neuropathy, CAD: Congenital autonomic dysfunction with universal pain loss.